02163nas a2200301 4500008004100000245007600041210006900117300001200186490000800198520129700206100001601503700001801519700002001537700001701557700001701574700001701591700001701608700001701625700001301642700001801655700001701673700002601690700001701716700001701733700001101750700002001761856008001781 2020 eng d00aMass ratio effects underlie ecosystem responses to environmental change0 aMass ratio effects underlie ecosystem responses to environmental a855-8640 v1083 a

1. Random species loss has been shown experimentally to reduce ecosystem function, sometimes more than other anthropogenic environmental changes. Yet, controversy surrounds the importance of this finding for natural systems where species loss is non‐random.
2. We compiled data from 16 multi‐year experiments located at a single native tallgrass prairie site. These experiments included responses to 11 anthropogenic environmental changes, as well as non‐random biodiversity loss either the removal of uncommon/rare plant species or the most common (dominant) species.
3. As predicted by the mass ratio hypothesis, loss of a dominant species had large impacts on productivity that were comparable to other anthropogenic drivers. In contrast, the loss of uncommon/rare species had small effects on productivity despite having the largest effects on species richness.
4. The anthropogenic drivers that had the largest effects on productivity nitrogen, irrigation, and fire experienced not only loss of species but also significant changes in the abundance and identity of dominant species.
5. Synthesis. These results suggest that mass ratio effects, rather than species loss per se, are an important determinant of ecosystem function with environmental change.

1 aSmith, M.D.1 aKoerner, S.E.1 aKnapp, Alan, K.1 aAvolio, M.L.1 aChaves, F.A.1 aDenton, E.M.1 aDietrich, J.1 aGibson, D.J.1 aGray, J.1 aHoffman, A.M.1 aHoover, D.L.1 aKomatsu, Kimberly, J.1 aSilletti, A.1 aWilcox, K.R.1 aYu, Q.1 aBlair, John, M. uhttps://besjournals.onlinelibrary.wiley.com/doi/abs/10.1111/1365-2745.1333002122nas a2200169 4500008004100000022001400041245011900055210006900174300001200243490000700255520154600262100002301808700002301831700001601854700002001870856006201890 2020 eng d a1354-101300aPrecipitation amount and event size interact to reduce ecosystem functioning during dry years in a mesic grassland0 aPrecipitation amount and event size interact to reduce ecosystem a658-6680 v263 a

Ongoing intensification of the hydrological cycle is altering rainfall regimes by increasing the frequency of extreme wet and dry years and the size of individual rainfall events. Despite long‐standing recognition of the importance of precipitation amount and variability for most terrestrial ecosystem processes, we lack understanding of their interactive effects on ecosystem functioning. We quantified this interaction in native grassland by experimentally eliminating temporal variability in growing season rainfall over a wide range of precipitation amounts, from extreme wet to dry conditions. We contrasted the rain use efficiency (RUE) of above‐ground net primary productivity (ANPP) under conditions of experimentally reduced versus naturally high rainfall variability using a 32‐year precipitation–ANPP dataset from the same site as our experiment. We found that increased growing season rainfall variability can reduce RUE and thus ecosystem functioning by as much as 42% during dry years, but that such impacts weaken as years become wetter. During low precipitation years, RUE is lowest when rainfall event sizes are relatively large, and when a larger proportion of total rainfall is derived from large events. Thus, a shift towards precipitation regimes dominated by fewer but larger rainfall events, already documented over much of the globe, can be expected to reduce the functioning of mesic ecosystems primarily during drought, when ecosystem processes are already compromised by low water availability.

1 aFelton, Andrew, J.1 aSlette, Ingrid, J.1 aSmith, M.D.1 aKnapp, Alan, K. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.1478902916nas a2200229 4500008004100000245008900041210006900130300001100199490000700210520219900217100001702416700001602433700002402449700002602473700001802499700001702517700001802534700002602552700001602578700001702594856007502611 2019 eng d00aA comprehensive approach to analyzing community dynamics using rank abundance curves0 acomprehensive approach to analyzing community dynamics using ran ae028810 v103 a

Univariate and multivariate methods are commonly used to explore the spatial and temporaldynamics of ecological communities, but each has limitations, including oversimplification or abstractionof communities. Rank abundance curves (RACs) potentially integrate these existing methodologies bydetailing species-level community changes. Here, we had three goals:first, to simplify analysis of commu-nity dynamics by developing a coordinated set of R functions, and second, to demystify the relationshipsamong univariate, multivariate, and RACs measures, and examine how each is influenced by the commu-nity parameters as well as data collection methods. We developed new functions for studying temporalchanges and spatial differences in RACs in an update to the R package library(“codyn”), alongside othernew functions to calculate univariate and multivariate measures of community dynamics. We also devel-oped a new approach to studying changes in the shape of RAC curves. The R package update presentedhere increases the accessibility of univariate and multivariate measures of community change over timeand difference over space. Next, we use simulated and real data to assess the RAC and multivariate mea-sures that are output from our new functions, studying (1) if they are influenced by species richness andevenness, temporal turnover, and spatial variability and (2) how the measures are related to each other.Lastly, we explore the use of the measures with an example from a long-term nutrient addition experiment.Wefind that the RAC and multivariate measures are not sensitive to species richness and evenness andthat all the measures detail unique aspects of temporal change or spatial differences. We alsofind that spe-cies reordering is the strongest correlate of a multivariate measure of compositional change and explainsmost community change observed in long-term nutrient addition experiment. Overall, we show that spe-cies reordering is potentially an understudied determinant of community changes over time or differencesbetween treatments. The functions developed here should enhance the use of RACs to further explore thedynamics of ecological communities.

1 aAvolio, M.L.1 aCarroll, I.1 aCollins, Scott., L.1 aHouseman, Gregory, R.1 aHallett, L.M.1 aIsbell, F.L.1 aKoerner, S.E.1 aKomatsu, Kimberly, J.1 aSmith, M.D.1 aWilcox, K.R. uhttps://esajournals.onlinelibrary.wiley.com/doi/epdf/10.1002/ecs2.288101740nas a2200181 4500008004100000245003400041210003400075300001600109490000800125520122500133100001701358700002901375700002301404700002801427700002501455700001601480856006201496 2019 eng d00aDemystifying dominant species0 aDemystifying dominant species a1106 - 11260 v2233 a

The pattern of a few abundant species and many rarer species is a defining characteristic of communities worldwide. These abundant species are often referred to as dominant species. Yet, despite their importance, the term dominant species is poorly defined and often used to convey different information by different authors. Based on a review of historical and contemporary definitions we develop a synthetic definition of dominant species. This definition incorporates the relative local abundance of a species, its ubiquity across the landscape, and its impact on community and ecosystem properties. A meta‐analysis of removal studies shows that the loss of species identified as dominant by authors can significantly impact ecosystem functioning and community structure. We recommend two metrics that can be used jointly to identify dominant species in a given community and provide a roadmap for future avenues of research on dominant species. In our review, we make the case that the identity and effects of dominant species on their environments are key to linking patterns of diversity to ecosystem function, including predicting impacts of species loss and other aspects of global change on ecosystems.

1 aAvolio, M.L.1 aForrestel, Elisabeth, J.1 aChang, Cynthia, C.1 aLa Pierre, Kimberly, J.1 aBurghardt, Karin, T.1 aSmith, M.D. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/nph.1578904634nas a2201021 4500008004100000245011700041210006900158300001600227490000800243520186900251100002602120700001702146700002402163700001902187700001702206700002602223700002302249700001802272700001702290700002202307700001902329700001402348700001502362700002402377700001402401700002202415700001702437700002002454700001802474700001702492700002102509700002802530700001702558700002402575700002202599700002602621700002102647700001802668700002402686700002402710700001102734700001902745700001902764700001502783700001402798700001402812700001802826700001202844700001602856700001902872700001902891700001602910700001902926700002002945700002002965700002202985700001103007700001403018700001903032700002403051700002303075700001703098700002503115700001903140700001803159700002003177700001603197700002403213700001803237700001503255700001903270700001603289700003203305700001603337700001703353700001703370700001603387700001803403700001703421700001903438700001403457700001503471700001703486700001103503700001903514700001803533856006103551 2019 eng d00aGlobal change effects on plant communities are magnified by time and the number of global change factors imposed0 aGlobal change effects on plant communities are magnified by time a17867-178730 v1163 a

Global change drivers (GCDs) are expected to alter community structure and consequently, the services that ecosystems provide. Yet, few experimental investigations have examined effects of GCDs on plant community structure across multiple ecosystem types, and those that do exist present conflicting patterns. In an unprecedented global synthesis of over 100 experiments that manipulated factors linked to GCDs, we show that herbaceous plant community responses depend on experimental manipulation length and number of factors manipulated. We found that plant communities are fairly resistant to experimentally manipulated GCDs in the short term (<10 y). In contrast, long-term (≥10 y) experiments show increasing community divergence of treatments from control conditions. Surprisingly, these community responses occurred with similar frequency across the GCD types manipulated in our database. However, community responses were more common when 3 or more GCDs were simultaneously manipulated, suggesting the emergence of additive or synergistic effects of multiple drivers, particularly over long time periods. In half of the cases, GCD manipulations caused a difference in community composition without a corresponding species richness difference, indicating that species reordering or replacement is an important mechanism of community responses to GCDs and should be given greater consideration when examining consequences of GCDs for the biodiversity–ecosystem function relationship. Human activities are currently driving unparalleled global changes worldwide. Our analyses provide the most comprehensive evidence to date that these human activities may have widespread impacts on plant community composition globally, which will increase in frequency over time and be greater in areas where communities face multiple GCDs simultaneously.

1 aKomatsu, Kimberly, J.1 aAvolio, M.L.1 aLemoine, Nathan, P.1 aIsbell, Forest1 aGrman, Emily1 aHouseman, Gregory, R.1 aKoerner, Sally, E.1 aJohnson, D.S.1 aWilcox, K.R.1 aAlatalo, Juha, M.1 aAnderson, J.P.1 aAerts, R.1 aBaer, S.G.1 aBaldwin, Andrew, H.1 aBates, J.1 aBeierkuhnlein, C.1 aBelote, R.T.1 aBlair, John, M.1 aBloor, J.M.G.1 aBohlen, P.J.1 aBork, Edward, W.1 aBoughton, Elizabeth, H.1 aBowman, W.D.1 aBritton, Andrea, J.1 aCahill, James, F.1 aChaneton, Enrique, J.1 aChiariello, N.R.1 aCheng, Jimin.1 aCollins, Scott., L.1 aCornelissen, J.H.C.1 aDu, G.1 aEskelinen, Anu1 aFirn, Jennifer1 aFoster, B.1 aGough, L.1 aGross, K.1 aHallett, L.M.1 aHan, X.1 aHarmens, H.1 aHovenden, M.J.1 aJagerbrand, A.1 aJentsch, A.1 aKern, Christel1 aKlanderud, Kari1 aKnapp, Alan, K.1 aKreyling, Juergen1 aLi, W.1 aLuo, Yiqi1 aMcCulley, R.L.1 aMcLaren, Jennie, R.1 aMegonigal, Patrick1 aMorgan, J.W.1 aOnipchenko, Vladimir1 aPennings, S.C.1 aPrevéy, J.S.1 aPrice, Jodi, N.1 aReich, P.B.1 aRobinson, Clare, H.1 aRussell, L.F.1 aSala, O.E.1 aSeabloom, E.W.1 aSmith, M.D.1 aSoudzilovskaia, Nadejda, A.1 aSouza, Lara1 aSuding, K.N.1 aSuttle, B.K.1 aSvejcar, T.1 aTilman, David1 aTognetti, P.1 aTurkington, R.1 aWhite, S.1 aXu, Zhuwen1 aYahdjian, L.1 aYu, Q.1 aZhang, Pengfei1 aZhang, Yunhai uhttps://www.pnas.org/content/early/2019/08/14/181902711602738nas a2200205 4500008004100000245006300041210006200104300001600166490000700182520212900189100002302318700002102341700001402362700001702376700002202393700001902415700001602434700002002450856006202470 2019 eng d00aHow ecologists define drought, and why we should do better0 aHow ecologists define drought and why we should do better a3193 - 32000 v253 a

Drought, widely studied as an important driver of ecosystem dynamics, is predicted to increase in frequency and severity globally. To study drought, ecologists must define or at least operationalize what constitutes a drought. How this is accomplished in practice is unclear, particularly given that climatologists have long struggled to agree on definitions of drought, beyond general variants of “an abnormal deficiency of water.” We conducted a literature review of ecological drought studies (564 papers) to assess how ecologists describe and study drought. We found that ecologists characterize drought in a wide variety of ways (reduced precipitation, low soil moisture, reduced streamflow, etc.), but relatively few publications (~32%) explicitly define what are, and are not, drought conditions. More troubling, a surprising number of papers (~30%) simply equated “dry conditions” with “drought” and provided little characterization of the drought conditions studied. For a subset of these, we calculated Standardized Precipitation Evapotranspiration Index values for the reported drought periods. We found that while almost 90% of the studies were conducted under conditions quantifiable as slightly to extremely drier than average, ~50% were within the range of normal climatic variability. We conclude that the current state of the ecological drought literature hinders synthesis and our ability to draw broad ecological inferences because drought is often declared but is not explicitly defined or well characterized. We suggest that future drought publications provide at least one of the following: (a) the climatic context of the drought period based on long‐term records; (b) standardized climatic index values; (c) published metrics from drought‐monitoring organizations; (d) a quantitative definition of what the authors consider to be drought conditions for their system. With more detailed and consistent quantification of drought conditions, comparisons among studies can be more rigorous, increasing our understanding of the ecological effects of drought.

1 aSlette, Ingrid, J.1 aPost, Alison, K.1 aAwad, Mai1 aEven, Trevor1 aPunzalan, Arianna1 aWilliams, Sere1 aSmith, M.D.1 aKnapp, Alan, K. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.1474703509nas a2200313 4500008004100000245008500041210006900126300001600195490000800211520253200219653000902751653001902760653003002779653001202809653002502821653002802846100003002874700002102904700002402925700002402949700002102973700002302994700002403017700001603041700002503057700002003082700001703102856007603119 2019 eng d00aShifts in plant functional composition following long-term drought in grasslands0 aShifts in plant functional composition following longterm drough a2133 - 21480 v1073 a

 1. Plant traits can provide unique insights into plant performance at the community scale. Functional composition, defined by both functional diversity and community-weighted trait means (CWMs), can affect the stability of above‐ground net primary production (ANPP) in response to climate extremes. Further complexity arises, however, when functional composition itself responds to environmental change. The duration of climate extremes, such as drought, is expected to increase with rising global temperatures; thus, understanding the impacts of long-term drought on functional composition and the corresponding effect that has on ecosystem function could improve predictions of ecosystem sensitivity to climate change.
 2. We experimentally reduced growing season precipitation by 66% across six temperate grasslands for 4 years and measured changes in three indices of functional diversity (functional dispersion, richness and evenness), community-weighted trait means and phylogenetic diversity (PD). Specific leaf area (SLA), leaf nitrogen content (LNC) and (at most sites) leaf turgor loss point (πTLP) were measured for species cumulatively representing ~90% plant cover at each site.
 3. Long-term drought led to increased community functional dispersion in three sites, with negligible effects on the remaining sites. Species re-ordering following the mortality/senescence of dominant species was the main driver of increased functional dispersion. The response of functional diversity was not consistently matched by changes in phylogenetic diversity. Community-level drought strategies (assessed as CWMs) largely shifted from drought tolerance to drought avoidance and/or escape strategies, as evidenced by higher community-weighted πTLP, SLA and LNC. Lastly, ecosystem drought sensitivity (i.e. relative reduction in ANPP in drought plots) was positively correlated with community-weighted SLA and negatively correlated with functional diversity.
 4. Synthesis. Increased functional diversity following long-term drought may stabilize ecosystem functioning in response to future drought. However, shifts in community-scale drought strategies may increase ecosystem drought sensitivity, depending on the nature and timing of drought. Thus, our results highlight the importance of considering both functional diversity and abundance‐weighted traits means of plant communities as their collective effect may either stabilize or enhance ecosystem sensitivity to drought.

10aANPP10aClimate change10acommunity weighted traits10aDrought10aFunctional diversity10aplant functional traits1 aGriffin-Nolan, Robert, J.1 aBlumenthal, D.M.1 aCollins, Scott., L.1 aFarkas, Timothy, E.1 aHoffman, Ava, M.1 aMueller, Kevin, E.1 aOcheltree, Troy, W.1 aSmith, M.D.1 aWhitney, Kenneth, D.1 aKnapp, Alan, K.1 aJones, Holly uhttps://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2745.1325202830nas a2200409 4500008004100000245011100041210006900152300001600221490000700237520170300244653001701947653001301964653001501977653002001992653001202012653001002024100001602034700001802050700002802068700001702096700001702113700001602130700001502146700001702161700001502178700001702193700002002210700001802230700001502248700001802263700001502281700001402296700001602310700001702326700001502343856006202358 2018 eng d00aAmbient changes exceed treatment effects on plant species abundance in long-term global change experiments0 aAmbient changes exceed treatment effects on plant species abunda a5668 - 56790 v243 a

The responses of species to environmental changes will determine future community composition and ecosystem function. Many syntheses of global change experiments examine the magnitude of treatment effect sizes, but we lack an understanding of how plant responses to treatments compare to ongoing changes in the unmanipulated (ambient or background) system. We used a database of long-term global change studies manipulating CO2 , nutrients, water, and temperature to answer three questions: (a) How do changes in plant species abundance in ambient plots relate to those in treated plots? (b) How does the magnitude of ambient change in species-level abundance over time relate to responsiveness to global change treatments? (c) Does the direction of species-level responses to global change treatments differ from the direction of ambient change? We estimated temporal trends in plant abundance for 791 plant species in ambient and treated plots across 16 long-term global change experiments yielding 2,116 experiment-species-treatment combinations. Surprisingly, for most species (57%) the magnitude of ambient change was greater than the magnitude of treatment effects. However, the direction of ambient change, whether a species was increasing or decreasing in abundance under ambient conditions, had no bearing on the direction of treatment effects. Although ambient communities are inherently dynamic, there is now widespread evidence that anthropogenic drivers are directionally altering plant communities in many ecosystems. Thus, global change treatment effects must be interpreted in the context of plant species trajectories that are likely driven by ongoing environmental changes.

10aelevated CO210anitrogen10aPhosphorus10aplant community10aWarming10awater1 aLangley, A.1 aChapman, S.K.1 aLa Pierre, Kimberly, J.1 aAvolio, M.L.1 aBowman, W.D.1 aJohnson, D.1 aIsbell, F.1 aWilcox, K.R.1 aFoster, B.1 aHovenden, M.1 aKnapp, Alan, K.1 aKoerner, S.E.1 aLortie, C.1 aMegonigal, J.1 aNewton, P.1 aReich, B.1 aSmith, M.D.1 aSuttle, B.K.1 aTilman, D. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.1444204101nas a2200613 4500008004100000245014300041210006900184300001600253490000700269520236400276100001602640700002002656700001902676700002002695700001702715700001802732700001602750700001602766700002002782700002402802700001202826700001602838700001702854700001802871700001702889700001702906700002602923700002202949700001902971700002102990700002203011700002103033700001703054700001903071700001503090700002303105700002703128700002003155700002103175700001803196700002103214700001803235700001503253700001803268700002203286700002503308700001903333700001803352700001903370700001403389700001703403700001803420856004903438 2018 eng d00aAsymmetric responses of primary productivity to altered precipitation simulated by ecosystem models across three long-term grassland sites0 aAsymmetric responses of primary productivity to altered precipit a3421 - 34370 v153 a

Field measurements of aboveground net primary productivity (ANPP) in temperate grasslands suggest that both positive and negative asymmetric responses to changes in precipitation (P) may occur. Under normal range of precipitation variability, wet years typically result in ANPP gains being larger than ANPP declines in dry years (positive asymmetry), whereas increases in ANPP are lower in magnitude in extreme wet years compared to reductions during extreme drought (negative asymmetry). Whether the current generation of ecosystem models with a coupled carbon–water system in grasslands are capable of simulating these asymmetric ANPP responses is an unresolved question. In this study, we evaluated the simulated responses of temperate grassland primary productivity to scenarios of altered precipitation with 14 ecosystem models at three sites: Shortgrass steppe (SGS), Konza Prairie (KNZ) and Stubai Valley meadow (STU), spanning a rainfall gradient from dry to moist. We found that (1) the spatial slopes derived from modeled primary productivity and precipitation across sites were steeper than the temporal slopes obtained from inter-annual variations, which was consistent with empirical data; (2) the asymmetry of the responses of modeled primary productivity under normal inter-annual precipitation variability differed among models, and the mean of the model ensemble suggested a negative asymmetry across the three sites, which was contrary to empirical evidence based on filed observations; (3) the mean sensitivity of modeled productivity to rainfall suggested greater negative response with reduced precipitation than positive response to an increased precipitation under extreme conditions at the three sites; and (4) gross primary productivity (GPP), net primary productivity (NPP), aboveground NPP (ANPP) and belowground NPP (BNPP) all showed concave-down nonlinear responses to altered precipitation in all the models, but with different curvatures and mean values. Our results indicated that most models overestimate the negative drought effects and/or underestimate the positive effects of increased precipitation on primary productivity under normal climate conditions, highlighting the need for improving eco-hydrological processes in those models in the future.

1 aWu, Donghai1 aCiais, Philippe1 aViovy, Nicolas1 aKnapp, Alan, K.1 aWilcox, K.R.1 aBahn, Michael1 aSmith, M.D.1 aVicca, Sara1 aFatichi, Simone1 aZscheischler, Jakob1 aHe, Yue1 aLi, Xiangyi1 aIto, Akihiko1 aArneth, Almut1 aHarper, Anna1 aUkkola, Anna1 aPaschalis, Athanasios1 aPoulter, Benjamin1 aPeng, Changhui1 aRicciuto, Daniel1 aReinthaler, David1 aChen, Guangsheng1 aTian, Hanqin1 aGenet, élène1 aMao, Jiafu1 aIngrisch, Johannes1 aNabel, Julia, E. S. M.1 aPongratz, Julia1 aBoysen, Lena, R.1 aKautz, Markus1 aSchmitt, Michael1 aMeir, Patrick1 aZhu, Qiuan1 aHasibeder, R.1 aSippel, Sebastian1 aDangal, Shree, R. S.1 aSitch, Stephen1 aShi, Xiaoying1 aWang, Yingping1 aLuo, Yiqi1 aLiu, Yongwen1 aPiao, Shilong uhttps://www.biogeosciences.net/15/3421/2018/02697nas a2200193 4500008004100000245009100041210006900132300001000201520208500211653002102296653001202317653002302329653001302352653002102365100001702386700002002403700001602423856006402439 2018 eng d00aCarbon exchange responses of a mesic grassland to an extreme gradient of precipitation0 aCarbon exchange responses of a mesic grassland to an extreme gra a1 -123 a

Growing evidence indicates that ecosystem processes may be differentially sensitive to dry versus wet years, and that current understanding of how precipitation affects ecosystem processes may not be predictive of responses to extremes. In an experiment within a mesic grassland, we addressed this uncertainty by assessing responses of two key carbon exchange processes—aboveground net primary production (ANPP) and soil respiration (Rs) - to an extensive gradient of growing season precipitation. This gradient comprised 11 levels that specifically included extreme values in precipitation; defined as the 1st, 5th, 95th, and 99th percentiles of the 112-year climate record. Across treatments, our experimental precipitation gradient linearly increased soil moisture availability in the rooting zone (upper 20 cm). Relative to ANPP under nominal precipitation amounts (defined as between the 15th and 85th percentiles), the magnitude of ANPP responses were greatest to extreme increases in precipitation, with an underlying linear response to both precipitation and soil moisture gradients. By contrast, Rs exhibited marginally greater responses to dry versus wet extremes, with a saturating relationship best explaining responses of Rs to both precipitation and soil moisture. Our findings indicate a linear relationship between ANPP and precipitation after incorporating responses to precipitation extremes in the ANPP–precipitation relationship, yet in contrast saturating responses of Rs. As a result, current linear ANPP–precipitation relationships (up to ~ 1000 mm) within mesic grasslands appear to hold as appropriate benchmarks for ecosystems models, yet such models should incorporate nonlinearities in responses of Rs amid increased frequencies and magnitudes of precipitation extremes.

10aClimate extremes10aDrought10aPrimary production10aRainfall10asoil respiration1 aFelton, A.J.1 aKnapp, Alan, K.1 aSmith, M.D. uhttps://link.springer.com/article/10.1007/s00442-018-4284-204794nas a2201093 4500008004100000245007500041210006900116300001400185490000600199520170000205100001801905700001601923700002001939700001601959700001701975700002401992700002002016700001802036700002002054700001202074700001902086700002502105700001902130700001702149700001602166700001502182700001702197700001702214700001502231700001602246700001702262700001702279700002802296700001802324700001702342700002202359700001702381700002202398700001802420700002402438700002002462700002502482700003002507700002902537700002602566700002002592700003002612700002302642700001602665700001902681700002202700700002802722700002002750700002402770700003002794700002002824700002602844700002702870700000502897700002502902700001702927700002002944700002302964700001502987700002203002700002303024700002203047700002203069700001703091700002203108700002203130700003003152700002303182700002103205700002303226700002203249700002103271700002703292700002203319700002403341700001703365700003203382700002003414700001603434700003203450700002203482700002503504700001703529700002003546700002303566700001503589700002903604856006703633 2018 eng d00aChange in dominance determines herbivore effects on plant biodiversity0 aChange in dominance determines herbivore effects on plant biodiv a1925-19320 v23 a

Herbivores alter plant biodiversity (species richness) in many of the world’s ecosystems, but the magnitude and the direction of herbivore effects on biodiversity vary widely within and among ecosystems. One current theory predicts that herbivores enhance plant biodiversity at high productivity but have the opposite effect at low productivity. Yet, empirical support for the importance of site productivity as a mediator of these herbivore impacts is equivocal. Here, we synthesize data from 252 large-herbivore exclusion studies, spanning a 20-fold range in site productivity, to test an alternative hypothesis—that herbivore-induced changes in the competitive environment determine the response of plant biodiversity to herbivory irrespective of productivity. Under this hypothesis, when herbivores reduce the abundance (biomass, cover) of dominant species (for example, because the dominant plant is palatable), additional resources become available to support new species, thereby increasing biodiversity. By contrast, if herbivores promote high dominance by increasing the abundance of herbivory-resistant, unpalatable species, then resource availability for other species decreases reducing biodiversity. We show that herbivore-induced change in dominance, independent of site productivity or precipitation (a proxy for productivity), is the best predictor of herbivore effects on biodiversity in grassland and savannah sites. Given that most herbaceous ecosystems are dominated by one or a few species, altering the competitive environment via herbivores or by other means may be an effective strategy for conserving biodiversity in grasslands and savannahs globally.

1 aKoerner, S.E.1 aSmith, M.D.1 aBurkepile, D.E.1 aHanan, N.P.1 aAvolio, M.L.1 aCollins, Scott., L.1 aKnapp, Alan, K.1 aLemoine, N.P.1 aForrestel, E.J.1 aEby, S.1 aThompson, D.I.1 aAguado-Santacruz, G.1 aAnderson, J.P.1 aAnderson, M.1 aAngassa, A.1 aBagchi, S.1 aBakker, E.S.1 aBastin, Gary1 aBaur, L.E.1 aBeard, K.H.1 aBeever, E.A.1 aBohlen, P.J.1 aBoughton, Elizabeth, H.1 aCanestro, Don1 aCesa, Ariela1 aChaneton, Enrique1 aCheng, Jimin1 aD’Antonio, C.M.1 aDeleglise, C.1 aDembélé, Fadiala.1 aDorrough, Josh.1 aEldridge, David., J.1 aFernandez-Going, Barbara.1 aFernández-Lugo, Silvia.1 aFraser, Lauchlan., H.1 aFreedman, Bill.1 aGarcía-Salgado, Gonzalo.1 aGoheen, Jacob., R.1 aGuo, Liang.1 aHusheer, Sean.1 aKarembé, Moussa.1 aKnops, Johannes., M. H.1 aKraaij, Tineke.1 aKulmatiski, Andrew.1 aKytöviita, Minna-Maarit.1 aLezama, Felipe.1 aLoucougaray, Gregory.1 aLoydi, Dan, G. Milchun1 a1 aMilton, Suzanne., J.1 aMorgan, J.W.1 aMoxham, Claire.1 aNehring, Kyle., C.1 aOlff, Han.1 aPalmer, Todd., M.1 aRebollo, Salvador.1 aRiginos, Corinna.1 aRisch, Anita., C.1 aRueda, Marta1 aSankaran, Mahesh.1 aSasaki, Takehiro.1 aSchoenecker, Kathryn., A.1 aSchultz, Nick., L.1 aSchütz, Martin.1 aSchwabe, Angelika.1 aSiebert, Frances.1 aSmit, Christian.1 aStahlheber, Karen., A.1 aStorm, Christian.1 aStrong, Dustin., J.1 aSu, Jishuai.1 aTiruvaimozhi, Yadugiri., V.1 aTyler, Claudia.1 aVal, James.1 aVandegehuchte, Martijn., L.1 aVeblen, Kari., E.1 aVermeire, Lance., T.1 aWard, David.1 aWu, Jianshuang.1 aYoung, Truman., P.1 aYu, Qiang.1 aZelikova, Tamara., Jane. uhttps://www.nature.com/articles/s41559-018-0696-y#article-info02255nas a2200145 4500008004100000245011300041210006900154300001000223520176500233100002101998700001702019700002002036700001602056856003702072 2018 eng d00aCodominant grasses differ in gene expression under experimental climate extremes in native tallgrass prairie0 aCodominant grasses differ in gene expression under experimental  ae43943 a

Extremes in climate, such as heat waves and drought, are expected to become more frequent and intense with forecasted climate change. Plant species will almost certainly differ in their responses to these stressors. We experimentally imposed a heat wave and drought in the tallgrass prairie ecosystem near Manhattan, Kansas, USA to assess transcriptional responses of two ecologically important C4 grass species, Andropogon gerardii and Sorghastrum nutans. Based on previous research, we expected that S. nutans would regulate more genes, particularly those related to stress response, under high heat and drought. Across all treatments, S. nutans showed greater expression of negative regulatory and catabolism genes while A. gerardii upregulated cellular and protein metabolism. As predicted, S. nutans showed greater sensitivity to water stress, particularly with downregulation of non-coding RNAs and upregulation of water stress and catabolism genes. A. gerardii was less sensitive to drought, although A. gerardii tended to respond with upregulation in response to drought versus S. nutans which downregulated more genes under drier conditions. Surprisingly, A. gerardii only showed minimal gene expression response to increased temperature, while S. nutans showed no response. Gene functional annotation suggested that these two species may respond to stress via different mechanisms. Specifically, A. gerardii tends to maintain molecular function while S. nutans prioritizes avoidance. Sorghastrum nutans may strategize abscisic acid response and catabolism to respond rapidly to stress. These results have important implications for success of these two important grass species under a more variable and extreme climate forecast for the future.

1 aHoffman, Ava, M.1 aAvolio, M.L.1 aKnapp, Alan, K.1 aSmith, M.D. uhttps://peerj.com/articles/4394/02813nas a2200217 4500008004100000245012300041210006900164300001600233490000700249520207200256100002302328700002402351700003002375700001902405700002502424700002702449700001602476700002002492700002102512856006202533 2018 eng d00aDrought consistently alters the composition of soil fungal and bacterial communities in grasslands from two continents0 aDrought consistently alters the composition of soil fungal and b a2818 - 28270 v243 a

The effects of short‐term drought on soil microbial communities remain largely unexplored, particularly at large scales and under field conditions. We used seven experimental sites from two continents (North America and Australia) to evaluate the impacts of imposed extreme drought on the abundance, community composition, richness, and function of soil bacterial and fungal communities. The sites encompassed different grassland ecosystems spanning a wide range of climatic and soil properties. Drought significantly altered the community composition of soil bacteria and, to a lesser extent, fungi in grasslands from two continents. The magnitude of the fungal community change was directly proportional to the precipitation gradient. This greater fungal sensitivity to drought at more mesic sites contrasts with the generally observed pattern of greater drought sensitivity of plant communities in more arid grasslands, suggesting that plant and microbial communities may respond differently along precipitation gradients. Actinobateria, and Chloroflexi, bacterial phyla typically dominant in dry environments, increased their relative abundance in response to drought, whereas Glomeromycetes, a fungal class regarded as widely symbiotic, decreased in relative abundance. The response of Chlamydiae and Tenericutes, two phyla of mostly pathogenic species, decreased and increased along the precipitation gradient, respectively. Soil enzyme activity consistently increased under drought, a response that was attributed to drought‐induced changes in microbial community structure rather than to changes in abundance and diversity. Our results provide evidence that drought has a widespread effect on the assembly of microbial communities, one of the major drivers of soil function in terrestrial ecosystems. Such responses may have important implications for the provision of key ecosystem services, including nutrient cycling, and may result in the weakening of plant–microbial interactions and a greater incidence of certain soil‐borne diseases.

1 aOchoa-Hueso, Raúl1 aCollins, Scott., L.1 aDelgado-Baquerizo, Manuel1 aHamonts, Kelly1 aPockman, William, T.1 aSinsabaugh, Robert, L.1 aSmith, M.D.1 aKnapp, Alan, K.1 aPower, Sally, A. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.1411302043nas a2200133 4500008004100000245007200041210006900113300001200182490000700194520160200201100002101803700001601824856006901840 2018 eng d00aGene expression differs in codominant prairie grasses under drought0 aGene expression differs in codominant prairie grasses under drou a334-3460 v183 a

Grasslands of the Central US are expected to experience severe droughts and other climate extremes in the future, yet we know little about how these grasses will respond in terms of gene expression. We compared gene expression in Andropogon gerardii and Sorghastrum nutans, two closely related co-dominant C4 grasses responsible for the majority of ecosystem function, using RNA-seq. We compared Trinity assemblies within each species to determine annotated functions of transcripts responding to drought. Subsequently, we compared homologous annotated gene-groups across the two species using cross-species meta-level analysis and functional clustering based on key terms. The majority of variation was found between species, as opposed to between drought and watered treatments. However, there is evidence for differential responses; Andropogon allocated gene expression differently compared to Sorghastrum, suggesting Andropogon focuses on stress alleviation (such as oxygen radical scavenging) rather than prevention. In contrast, Sorghastrum may employ a drought avoidance strategy by modulating osmotic response, especially with hormonal regulation. We found Sorghastrum tended to be more sensitive within 10 key gene-groups related to stress, abscisic acid, and trichomes, suggesting gene expression may mechanistically parallel sensitivity at the physiological level. Our findings corroborate phenotypic and physiological differences in the field, and may help explain the phenotypic mechanisms of these two species in the tallgrass prairie community under future drought scenarios.

1 aHoffman, Ava, M.1 aSmith, M.D. uhttps://onlinelibrary.wiley.com/doi/full/10.1111/1755-0998.1273302388nas a2200205 4500008004100000022001400041245010800055210006900163300001400232490000800246520170300254100003001957700002801987700002202015700002602037700002402063700001602087700002002103856005902123 2018 eng d a1385-023700aLegacy effects of a regional drought on aboveground net primary production in six central US grasslands0 aLegacy effects of a regional drought on aboveground net primary  a505 - 5150 v2193 a

Global climate models predict increases in the frequency and severity of drought worldwide, directly affecting most ecosystem types. Consequently, drought legacy effects (drought-induced alterations in ecosystem function postdrought) are expected to become more common in ecosystems varying from deserts to grasslands to forests. Drought legacies in grasslands are usually negative and reduce ecosystem function, particularly after extended drought. Moreover, ecosystems that respond strongly to drought (high sensitivity) might be expected to exhibit the largest legacy effects the next year, but this relationship has not been established. We quantified legacy effects of a severe regional drought in 2012 on postdrought (2013) aboveground net primary productivity (ANPP) in six central US grasslands. We predicted that (1) the magnitude of drought legacy effects measured in 2013 would be positively related to the sensitivity of ANPP to the 2012 drought, and (2) drought legacy effects would be negative (reducing 2013 ANPP relative to that expected given normal precipitation amounts). The magnitude of legacy effects measured in 2013 was strongly related (r2 = 0.88) to the sensitivity of ANPP to the 2012 drought across these six grasslands. However, contrary to expectations, positive legacy effects (greater than expected ANPP) were more commonly observed than negative legacy effects. Thus, while the sensitivity of ANPP to drought may be a useful predictor of the magnitude of legacy effects, short-term (1-year) severe droughts may cause legacy effects that are more variable than those observed after multiyear droughts.

1 aGriffin-Nolan, Robert, J.1 aCarroll, Charles, J. W.1 aDenton, Elsie, M.1 aJohnston, Melissa, K.1 aCollins, Scott., L.1 aSmith, M.D.1 aKnapp, Alan, K. uhttp://link.springer.com/10.1007/s11258-018-0813-7.pdf02291nas a2200145 4500008004100000245011600041210006900157300001100226490000800237520179100245100001702036700002102053700001602074856005502090 2018 eng d00aLinking gene regulation, physiology, and plant biomass allocation in Andropogon gerardii in response to drought0 aLinking gene regulation physiology and plant biomass allocation  a1 - 150 v2193 a

Plant responses to drought are often initiated at the molecular level and cascade upwards to affect physiology and growth. How plants respond to and recover from drought have consequences for their growth and survival in drier climates predicted with climate change. We studied four ecologically relevant genotypes of a common C4 grass, Andropogon gerardii. These genotypes had differential responses to a decade of more variable precipitation patterns in a field experiment in native tallgrass prairie. Here, we conducted a greenhouse experiment examining how these genotypes responded to repeated 10-day drought-recovery cycles when experiencing either a severe or moderate drought. We did this twice over the course of the experiment, early, after 5 weeks, and late, after 9 weeks of drought. We studied nine genes involved in water stress signaling and drought response in leaf tissue using real-time reverse-transcriptase polymerase chain reaction (qRT-PCR). We also measured photosynthesis, stomatal conductance, and biomass accumulation and allocation. In early drought, we found consistent differences among genotypes in gene expression, leaf-level physiology, and biomass accumulation and allocation. We found genes involved in ABA, proline synthesis, and mitigating oxidative stress were differentially expressed between genotypes, while genes that coded for aquaporins and chaperones were not. In late drought, we found fewer overall differences, and little regulation of drought responsive genes. Ultimately, we found genotypes either had greater phenotypic plasticity, suggesting an ability to avoid drought and maximize water resources when they were present, or genotypes were better at tolerating drought.

1 aAvolio, M.L.1 aHoffman, Ava, M.1 aSmith, M.D. uhttp://link.springer.com/10.1007/s11258-017-0773-303418nas a2200301 4500008004100000245010300041210006900144300001400213490000800227520246100235100002202696700002302718700002402741700001702765700001602782700002302798700001802821700002202839700002802861700001802889700002202907700002302929700002202952700002302974700002702997700001603024856007603040 2018 eng d00aMean annual precipitation predicts primary production resistance and resilience to extreme drought0 aMean annual precipitation predicts primary production resistance a360 - 3660 v6363 a

Extreme drought is increasing in frequency and intensity in many regions globally, with uncertain consequences for the resistance and resilience of ecosystem functions, including primary production. Primary production resistance, the capacity to withstand change during extreme drought, and resilience, the degree to which production recovers, vary among and within ecosystem types, obscuring generalized patterns of ecological stability. Theory and many observations suggest forest production is more resistant but less resilient than grassland production to extreme drought; however, studies of production sensitivity to precipitation variability indicate that the processes controlling resistance and resilience may be influenced more by mean annual precipitation (MAP) than ecosystem type. Here, we conducted a global meta-analysis to investigate primary production resistance and resilience to extreme drought in 64 forests and grasslands across a broad MAP gradient. We found resistance to extreme drought was predicted by MAP; however, grasslands (positive) and forests (negative) exhibited opposing resilience relationships with MAP. Our findings indicate that common plant physiological mechanisms may determine grassland and forest resistance to extreme drought, whereas differences among plant residents in turnover time, plant architecture, and drought adaptive strategies likely underlie divergent resilience patterns. The low resistance and resilience of dry grasslands suggests that these ecosystems are the most vulnerable to extreme drought – a vulnerability that is expected to compound as extreme drought frequency increases in the future.

 

1 aHaëntjens, Ellen1 aDe Boeck, Hans, J.1 aLemoine, Nathan, P.1 aMänd, Pille1 aDulay, K.G.1 aSchmidt, Inger, K.1 aJentsch, Anke1 aStampfli, Andreas1 aAnderegg, William, R.L.1 aBahn, Michael1 aKreyling, Juergen1 aWohlgemuth, Thomas1 aLloret, Francisco1 aClassen, T.Aimée.1 aGough, Christopher, M.1 aSmith, M.D. uhttps://www.sciencedirect.com/science/article/abs/pii/S004896971831467002332nas a2200265 4500008004100000245008400041210006900125300001400194490000700208520155900215100002001774700002001794700002401814700001701838700001701855700001301872700001701885700001301902700001801915700001801933700001201951700001301963700001601976856007401992 2018 eng d00aA reality check for climate change experiments: Do they reflect the real world?0 areality check for climate change experiments Do they reflect the a2145-21510 v993 a

Experiments are widely used in ecology, particularly for assessing global change impacts on ecosystem function. However, results from experiments often are inconsistent with observations made under natural conditions, suggesting the need for rigorous comparisons of experimental and observational studies. We conducted such a “reality check” for a grassland ecosystem by compiling results from nine independently conducted climate change experiments. Each experiment manipulated growing season precipitation (GSP) and measured responses in aboveground net primary production (ANPP). We compared results from experiments with long‐term (33‐yr) annual precipitation and ANPP records to ask if collectively (n = 44 experiment‐years) experiments yielded estimates of ANPP, rain‐use efficiency (RUE, grams per square meter ANPP per mm precipitation), and the relationship between GSP and ANPP comparable to observations. We found that mean ANPP and RUE from experiments did not deviate from observations. Experiments and observational data also yielded similar functional relationships between ANPP and GSP, but only within the range of historically observed GSP. Fewer experiments imposed extreme levels of GSP (outside the observed 33‐yr record), but when these were included, they altered the GSP–ANPP relationship. This result underscores the need for more experiments imposing extreme precipitation levels to resolve how forecast changes in climate regimes will affect ecosystem function in the future.

1 aKnapp, Alan, K.1 aCarroll, C.J.W.1 aGriffin-Nolan, R.J.1 aSlette, I.J.1 aChavez, F.A.1 aBaur, L.1 aFelton, A.J.1 aGray, J.1 aHoffman, A.M.1 aLemoine, N.P.1 aMao, W.1 aPost, A.1 aSmith, M.D. uhttps://esajournals.onlinelibrary.wiley.com/doi/epdf/10.1002/ecy.247400968nas a2200169 4500008004100000245010500041210006900146300001400215490000700229520040300236100001600639700001700655700002100672700002200693700002000715856006300735 2017 eng d00aAssessing community and ecosystem sensitivity to climate change - toward a more comparative approach0 aAssessing community and ecosystem sensitivity to climate change  a235 - 2370 v283 a

Plant communities can vary widely in their sensitivity to changing precipitation regimes, as reported by Byrne et al., Mulhouse et al. and Sternberg et al. in this issue of Journal of Vegetation Science. But to understand why communities differ in their sensitivity, we argue that clearly defined metrics of sensitivity and coordinated research approaches are needed to elucidate mechanisms.

1 aSmith, M.D.1 aWilcox, K.R.1 aPower, Sally, A.1 aTissue, David, T.1 aKnapp, Alan, K. uhttps://onlinelibrary.wiley.com/doi/full/10.1111/jvs.1252403566nas a2200421 4500008004100000245014000041210006900181260001400250490000700264520229900271100001702570700001502587700002702602700002402629700002302653700002202676700001702698700002102715700001802736700002402754700001702778700002102795700001602816700001702832700002002849700001902869700001702888700002702905700002102932700002502953700001602978700001802994700002303012700002003035700001303055700001403068856006203082 2017 eng d00aAsymmetric responses of primary productivity to precipitation extremes: A synthesis of grassland precipitation manipulation experiments0 aAsymmetric responses of primary productivity to precipitation ex c4376-43850 v233 a

Climatic changes are altering Earth's hydrological cycle, resulting in altered precipitation amounts, increased interannual variability of precipitation, and more frequent extreme precipitation events. These trends will likely continue into the future, having substantial impacts on net primary productivity (NPP) and associated ecosystem services such as food production and carbon sequestration. Frequently, experimental manipulations of precipitation have linked altered precipitation regimes to changes in NPP. Yet, findings have been diverse and substantial uncertainty still surrounds generalities describing patterns of ecosystem sensitivity to altered precipitation. Additionally, we do not know whether previously observed correlations between NPP and precipitation remain accurate when precipitation changes become extreme. We synthesized results from 83 case studies of experimental precipitation manipulations in grasslands worldwide. We used meta-analytical techniques to search for generalities and asymmetries of aboveground NPP (ANPP) and belowground NPP (BNPP) responses to both the direction and magnitude of precipitation change. Sensitivity (i.e., productivity response standardized by the amount of precipitation change) of BNPP was similar under precipitation additions and reductions, but ANPP was more sensitive to precipitation additions than reductions; this was especially evident in drier ecosystems. Additionally, overall relationships between the magnitude of productivity responses and the magnitude of precipitation change were saturating in form. The saturating form of this relationship was likely driven by ANPP responses to very extreme precipitation increases, although there were limited studies imposing extreme precipitation change, and there was considerable variation among experiments. This highlights the importance of incorporating gradients of manipulations, ranging from extreme drought to extreme precipitation increases into future climate change experiments. Additionally, policy and land management decisions related to global change scenarios should consider how ANPP and BNPP responses may differ, and that ecosystem responses to extreme events might not be predicted from relationships found under moderate environmental changes.

1 aWilcox, K.R.1 aShi, Zheng1 aGherardi, Laureano, A.1 aLemoine, Nathan, P.1 aKoerner, Sally, E.1 aHoover, David, L.1 aBork, Edward1 aByrne, Kerry, M.1 aCahill, James1 aCollins, Scott., L.1 aEvans, Sarah1 aGilgen, Anna, K.1 aHolub, Petr1 aJiang, Lifen1 aKnapp, Alan, K.1 aLeCain, Daniel1 aLiang, Junyi1 aGarcia-Palacios, Pablo1 aPeñuelas, Josep1 aPockman, William, T.1 aSmith, M.D.1 aSun, Shanghua1 aWhite, Shannon, R.1 aYahdjian, Laura1 aZhu, Kai1 aLuo, Yiqi uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.1370603310nas a2200733 4500008004100000245008800041210006900129520119600198653002001394653002201414653001901436653001701455653002001472653001501492653002201507653002501529653002201554100001701576700002701593700002301620700001701643700002401660700001701684700002801701700002601729700001901755700002701774700002201801700002401823700002101847700002801868700001701896700002401913700002201937700002401959700001101983700001901994700001702013700001802030700001902048700002002067700002002087700002202107700001402129700002402143700002302167700002502190700001902215700002002234700002402254700002202278700001602300700003202316700001602348700001802364700002302382700001502405700002002420700001402440700001902454700001802473700002302491856006202514 2017 eng d00aAsynchrony among local communities stabilises ecosystem function of metacommunities0 aAsynchrony among local communities stabilises ecosystem function3 a

Temporal stability of ecosystem functioning increases the predictability and reliability of ecosystem services, and understanding the drivers of stability across spatial scales is important for land management and policy decisions. We used species-level abundance data from 62 plant communities across five continents to assess mechanisms of temporal stability across spatial scales. We assessed how asynchrony (i.e. different units responding dissimilarly through time) of species and local communities stabilised metacommunity ecosystem function. Asynchrony of species increased stability of local communities, and asynchrony among local communities enhanced metacommunity stability by a wide range of magnitudes (1–315%); this range was positively correlated with the size of the metacommunity. Additionally, asynchronous responses among local communities were linked with species’ populations fluctuating asynchronously across space, perhaps stemming from physical and/or competitive differences among local communities. Accordingly, we suggest spatial heterogeneity should be a major focus for maintaining the stability of ecosystem services at larger spatial scales.

10aAlpha diversity10aalpha variability10abeta diversity10aBiodiversity10aCoRRE data base10apatchiness10aPlant communities10aPrimary productivity10aspecies synchrony1 aWilcox, K.R.1 aTredennick, Andrew, T.1 aKoerner, Sally, E.1 aGrman, Emily1 aHallett, Lauren, M.1 aAvolio, M.L.1 aLa Pierre, Kimberly, J.1 aHouseman, Gregory, R.1 aIsbell, Forest1 aJohnson, David, Samuel1 aAlatalo, Juha, M.1 aBaldwin, Andrew, H.1 aBork, Edward, W.1 aBoughton, Elizabeth, H.1 aBowman, W.D.1 aBritton, Andrea, J.1 aCahill, James, F.1 aCollins, Scott., L.1 aDu, G.1 aEskelinen, Anu1 aGough, Laura1 aJentsch, Anke1 aKern, Christel1 aKlanderud, Kari1 aKnapp, Alan, K.1 aKreyling, Juergen1 aLuo, Yiqi1 aMcLaren, Jennie, R.1 aMegonigal, Patrick1 aOnipchenko, Vladimir1 aPrevéy, Janet1 aPrice, Jodi, N.1 aRobinson, Clare, H.1 aSala, Osvaldo, E.1 aSmith, M.D.1 aSoudzilovskaia, Nadejda, A.1 aSouza, Lara1 aTilman, David1 aWhite, Shannon, R.1 aXu, Zhuwen1 aYahdjian, Laura1 aYu, Qiang1 aZhang, Pengfei1 aZhang, Yunhai1 aGurevitch, Jessica uhttp://onlinelibrary.wiley.com/doi/10.1111/ele.12861/epdf00487nas a2200121 4500008004100000245011000041210006900151260004800220490001400268100001500282700001600297856005200313 2017 eng d00aClimate change impacts on population dynamics in tallgrass prairie: implications for species codominance0 aClimate change impacts on population dynamics in tallgrass prair aFort Collins, CObColorado State University0 vMS Thesis1 aGray, J.E.1 aSmith, M.D. uhttps://mountainscholar.org/handle/10217/18143102351nas a2200241 4500008004100000022001400041245007700055210006900132300001400201490000800215520162000223653001701843653002301860653002201883653003001905100002901935700001901964700002301983700001702006700002702023700001602050856004302066 2017 eng d a0027-842400aDifferent clades and traits yield similar grassland functional responses0 aDifferent clades and traits yield similar grassland functional r a705 - 7100 v1143 aPlant functional traits are viewed as key to predicting important ecosystem and community properties across resource gradients within and among biogeographic regions. Vegetation dynamics and ecosystem processes, such as aboveground net primary productivity (ANPP), are increasingly being modeled as a function of the quantitative traits of species, which are used as proxies for photosynthetic rates and nutrient and water-use efficiency. These approaches rely on an assumption that a certain trait value consistently confers a specific function or response under given environmental conditions. Here, we provide a critical test of this idea and evaluate whether the functional traits that drive the well-known relationship between precipitation and ANPP differ between systems with distinct biogeographic histories and species assemblages. Specifically, we compared grasslands spanning a broad precipitation gradient (∼200–1,000 mm/y) in North America and South Africa that differ in the relative representation and abundance of grass phylogenetic lineages. We found no significant difference between the regions in the positive relationship between annual precipitation and ANPP, yet the trait values underlying this relationship differed dramatically. Our results challenge the trait-based approach to predicting ecosystem function by demonstrating that different combinations of functional traits can act to maximize ANPP in a given environmental setting. Further, we show the importance of incorporating biogeographic and phylogenetic history in predicting community and ecosystem properties using traits. 10abiogeography10aEcosystem function10aFunctional traits10agrasslands. phylogenetics1 aForrestel, Elisabeth, J.1 aDonoghue, M.J.1 aEdwards, Erika, J.1 aJetz, Walter1 aToit, Justin, C. O. du1 aSmith, M.D. uhttps://www.pnas.org/content/114/4/70502073nas a2200157 4500008004100000245009900041210006900140300001400209490000800223520153700231100002201768700002301790700001601813700002001829856006601849 2017 eng d00aDrought timing differentially affects above- and belowground productivity in a mesic grassland0 aDrought timing differentially affects above and belowground prod a317 - 3280 v2183 a

Climate models forecast an intensification of the global hydrological cycle with droughts becoming more frequent and severe, and shifting to times when they have been historically uncommon. Droughts, or prolonged periods of precipitation deficiency, are characteristic of most temperate grasslands, yet few experiments have explored how variation in the seasonal timing of drought may impact ecosystem function. We investigated the response of above- and belowground net primary production (ANPP & BNPP) to altered drought timing in a mesic grassland in NE Kansas. Moderate drought treatments (25% reduction from the mean growing season precipitation [GSP]) were imposed by erecting rainout shelters in late spring (LSP), early summer (ESM), and mid-summer (MSM, n = 10 plots/treatment). These treatments were compared to two controls (long-term average GSP [LTA] and ambient GSP [AMB]) and a wet treatment (+30% of the long-term average GSP [WET]). We found that LSP drought did not significantly reduce ANPP relative to control plots while the ESM and MSM drought did despite equivalent reductions in soil moisture. In contrast, the WET treatment did not affect ANPP. Neither the WET nor the drought treatments altered BNPP as compared to the controls. Our results suggest that forecasts of ecosystem responses to climate change will be improved if both the seasonal timing of alterations in precipitation as well as differential responses of above- and belowground productivity to drought are incorporated into models.

1 aDenton, Elsie, M.1 aDietrich, John, D.1 aSmith, M.D.1 aKnapp, Alan, K. uhttps://link.springer.com/article/10.1007%2Fs11258-016-0690-x02051nas a2200205 4500008004100000245011100041210006900152300001200221490000800233520138900241653002301630653002101653653001201674653001801686653002201704100001701726700002001743700001601763856006601779 2017 eng d00aPhotosynthetic responses of a dominant C4 grass to an experimental heat wave are mediated by soil moisture0 aPhotosynthetic responses of a dominant C4 grass to an experiment a303-3130 v1833 a

Extreme heat waves and drought are predicted to increase in frequency and magnitude with climate change. These extreme events often co-occur, making it difficult to separate their direct and indirect effects on important ecophysiological and carbon cycling processes such as photosynthesis. Here, we assessed the independent and interactive effects of experimental heat waves and drought on photosynthesis in Andropogon gerardii, a dominant C4 grass in a native mesic grassland. We experimentally imposed a two-week heat wave at four intensity levels under two contrasting soil moisture regimes: a well-watered control and an extreme drought. There were three main findings from this study. First, the soil moisture regimes had large effects on canopy temperature, leading to extremely high temperatures under drought and low temperatures under well-watered conditions. Second, soil moisture mediated the photosynthetic response to heat; heat reduced photosynthesis under the well-watered control, but not under the extreme drought treatment. Third, the effects of heat on photosynthesis appeared to be driven by a direct thermal effect, not indirectly through other environmental or ecophysiological variables. These results suggest that while photosynthesis in this dominant C4 grass is sensitive to heat stress, this sensitivity can be overwhelmed by extreme drought stress.

10aCanopy temperature10aClimate extremes10aDrought10aEcophysiology10atallgrass prairie1 aHoover, D.L.1 aKnapp, Alan, K.1 aSmith, M.D. uhttps://link.springer.com/article/10.1007%2Fs00442-016-3755-602567nas a2200133 4500008004100000245011400041210006900155260001600224520205400240100002402294700001902318700001602337856008002353 2017 eng d00aPrecipitation and environmental constraints on three aspects of flowering in three dominant tallgrass species0 aPrecipitation and environmental constraints on three aspects of  cMar-05-20183 a
  1. Flower production can comprise up to 70% of aboveground primary production in grasslands. Yet we know relatively little about how the environment and timing of rainfall determine flower productivity. Evidence suggests that deficits or additions of rainfall during phenlologically relevant periods (i.e. growth, storage, initiation of flowering, and reproduction) can determine flower production in grasslands.
  2. We used long-term data from the Konza Prairie LTER to test how fire, soil topography, and precipitation amounts during four phenologically relevant periods of the growing season constrain three aspects of flowering in three dominant C4 grass species. Specifically, we examined the probability of flowering, flowering stalk density, and individual flowering stalk biomass for Andropogon gerardii, Schizachyrium scoparium and Sorghastrum nutans.
  3. We found that each of the three species responded to the amount of precipitation during phenologically relevant periods in unique ways. All aspects of A. gerardii flowering were sensitive to precipitation during the flowering stalk elongation period (June 20 – Aug 3). The probability of S. nutans flowering was partly determined by precipitation during the rapid growth phase (April 21 – June 4), whereas flowering stalk density of this species depended on rainfall during flowering stalk elongation (June 20 – Aug 3). In contrast, all aspects of flowering of S. scoparium were relatively independent of rainfall during any period.
  4. Our results demonstrate that three functionally similar, codominant C4 grass species respond differently to phenologically relevant precipitation periods. As a result, drought during any phenological window during the growing season can adversely impact biomass and flowering production of grasslands via species-specific reductions in flowering stalk density and biomass.
1 aLemoine, Nathan, P.1 aDietrich, J.D.1 aSmith, M.D. uhttps://besjournals.onlinelibrary.wiley.com/doi/abs/10.1111/1365-2435.1290402136nas a2200145 4500008004100000245014700041210006900188300001300257490000700270520158800277100001301865700001801878700001601896856007801912 2017 eng d00aProspective evidence for independent nitrogen and phosphorus limitation of grasshopper (Chorthippus curtipennis) growth in a tallgrass prairie0 aProspective evidence for independent nitrogen and phosphorus lim ae01777540 v123 a

Insect herbivores play a pivotal role in regulating plant production and community composition, and their role in terrestrial ecosystems is partly determined by their feeding behavior and performance among plants of differing nutritional quality. Historically, nitrogen (N) has been considered the primary limiting nutrient of herbivorous insects, but N is only one of many potential nutrients important to insect performance. Of these nutrients, phosphorus (P) is perhaps the most important because somatic growth depends upon P-rich ribosomal RNA. Yet relatively few studies have assessed the strength of P-limitation for terrestrial insects and even fewer have simultaneously manipulated both N and P to assess the relative strengths of N- and P-limitation. Here, we tested for potential N and P limitation, as well as N:P co-limitation, on Chorthippis curtipennis (Orthoptera, Acrididae), an abundant member of arthropod communities of central US prairies. Our results demonstrate weak evidence for both N and P limitation of C. curtipennis growth rates in laboratory feeding assays. Importantly, P-limitation was just as strong as N-limitation, but we found no evidence for NP co-limitation in our study. Furthermore, nutrient limitation was not apparent in field studies, suggesting that insect growth rates may be predominately controlled by other factors, including temperature and predation. Our results suggest that P should be jointly considered, along with N, as a primary determinant of herbivore feeding behavior under both current and future climate conditions.

1 aRode, M.1 aLemoine, N.P.1 aSmith, M.D. uhttps://journals.plos.org/plosone/article?id=10.1371/journal.pone.017775403239nas a2200313 4500008004100000245011900041210006900160300001400229490000700243520231400250100002002564700001702584700001402601700002002615700002402635700001602659700001702675700002402692700001702716700001602733700001502749700001902764700001502783700001502798700001702813700001702830700001602847856006202863 2017 eng d00aPushing precipitation to the extremes in distributed experiments: recommendations for simulating wet and dry years0 aPushing precipitation to the extremes in distributed experiments a1774-17820 v233 a

Intensification of the global hydrological cycle, ranging from larger individual precipitation events to more extreme multiyear droughts, has the potential to cause widespread alterations in ecosystem structure and function. With evidence that the incidence of extreme precipitation years (defined statistically from historical precipitation records) is increasing, there is a clear need to identify ecosystems that are most vulnerable to these changes and understand why some ecosystems are more sensitive to extremes than others. To date, opportunistic studies of naturally occurring extreme precipitation years, combined with results from a relatively small number of experiments, have provided limited mechanistic understanding of differences in ecosystem sensitivity, suggesting that new approaches are needed. Coordinated distributed experiments (CDEs) arrayed across multiple ecosystem types and focused on water can enhance our understanding of differential ecosystem sensitivity to precipitation extremes, but there are many design challenges to overcome (e.g., cost, comparability, standardization). Here, we evaluate contemporary experimental approaches for manipulating precipitation under field conditions to inform the design of ‘Drought-Net’, a relatively low-cost CDE that simulates extreme precipitation years. A common method for imposing both dry and wet years is to alter each ambient precipitation event. We endorse this approach for imposing extreme precipitation years because it simultaneously alters other precipitation characteristics (i.e., event size) consistent with natural precipitation patterns. However, we do not advocate applying identical treatment levels at all sites – a common approach to standardization in CDEs. This is because precipitation variability varies >fivefold globally resulting in a wide range of ecosystem-specific thresholds for defining extreme precipitation years. For CDEs focused on precipitation extremes, treatments should be based on each site's past climatic characteristics. This approach, though not often used by ecologists, allows ecological responses to be directly compared across disparate ecosystems and climates, facilitating process-level understanding of ecosystem sensitivity to precipitation extremes.

1 aKnapp, Alan, K.1 aAvolio, M.L.1 aBeier, C.1 aCarroll, C.J.W.1 aCollins, Scott., L.1 aDukes, J.S.1 aFraser, L.H.1 aGriffin-Nolan, R.J.1 aHoover, D.L.1 aJentsch, A.1 aLoik, M.E.1 aPhillips, R.P.1 aPost, A.K.1 aSala, O.E.1 aSlette, I.J.1 aYahdjian, L.1 aSmith, M.D. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.1350401394nas a2200145 4500008004100000245011200041210006900153300001000222490000800232520089100240100002001131700001401151700001601165856006701181 2017 eng d00aReconciling inconsistencies in precipitation– productivity relationships: implications for climate change0 aReconciling inconsistencies in precipitation productivity relati a41-470 v2143 aPrecipitation (PPT) is a primary climatic determinant of plant growth and aboveground net primary production (ANPP) over much of the globe. Thus, PPT–ANPP relationships are important both ecologically and to land–atmosphere models that couple terrestrial vegetation to the global carbon cycle. Empirical PPT–ANPP relationships derived from long-term site-based data are almost always portrayed as linear, but recent evidence has accumulated that is inconsistent with an underlying linear relationship. We review, and then reconcile, these inconsistencies with a nonlinear model that incorporates observed asymmetries in PPT–ANPP relationships. Although data are currently lacking for parameterization, this new model highlights research needs that, when met, will improve our understanding of carbon cycle dynamics, as well as forecasts of ecosystem responses to climate change.1 aKnapp, Alan, K.1 aCiais, P.1 aSmith, M.D. uhttps://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.1438101743nas a2200145 4500008004100000245009500041210006900136520124400205100002201449700002401471700002001495700001601515700002001531856004601551 2016 eng d00aAltered rainfall patterns increase forb abundance and richness in native tallgrass prairie0 aAltered rainfall patterns increase forb abundance and richness i3 a

Models predict that precipitation variability will increase with climate change. We used a 15-year precipitation manipulation experiment to determine if altering the timing and amount of growing season rainfall will impact plant community structure in annually burned, native tallgrass prairie. The altered precipitation treatment maintained the same total growing season precipitation as the ambient precipitation treatment, but received a rainfall regime of fewer, larger rain events, and longer intervals between events each growing season. Although this change in precipitation regime significantly lowered mean soil water content, overall this plant community was remarkably resistant to altered precipitation with species composition relatively stable over time. However, we found significantly higher forb cover and richness and slightly lower grass cover on average with altered precipitation, but the forb responses were manifest only after a ten-year lag period. Thus, although community structure in this grassland is relatively resistant to this type of altered precipitation regime, forb abundance in native tallgrass prairie may increase in a future characterized by increased growing season precipitation variability.

1 aJones, Sydney, K.1 aCollins, Scott., L.1 aBlair, John, M.1 aSmith, M.D.1 aKnapp, Alan, K. uhttps://www.nature.com/articles/srep2012002040nas a2200157 4500008004100000245010500041210006900146300001200215490000700227520150000234100001701734700002001751700001601771700002001787856007501807 2016 eng d00aDoes ecosystem sensitivity to precipitation at the site-level conform to regional-scale predictions?0 aDoes ecosystem sensitivity to precipitation at the sitelevel con a561-5680 v973 a

Central to understanding global C cycle dynamics is the functional relationship between precipitation and net primary production (NPP). At large spatial (regional) scales, the responsiveness of aboveground NPP (ANPP) to inter-annual variation in annual precipitation (AP; ANPPsensitivity) is inversely related to site-level ANPP, coinciding with turnover of plant communities along precipitation gradients. Within ecosystems experiencing chronic alterations in water availability, plant community change will also occur with unknown consequences for ANPPsensitivity. To examine the role plant community shifts may play in determining alterations in site-level ANPPsensitivity, we experimentally increased precipitation by ~35% for two decades in a native Central US grassland. Consistent with regional models, ANPPsensitivity decreased initially as water availability and ANPP increased. However, ANPPsensitivity shifted back to ambient levels when mesic species increased in abundance in the plant community. Similarly, in grassland sites with distinct mesic and xeric plant communities and corresponding 50% differences in ANPP, ANPPsensitivity did not differ over almost three decades. We conclude that responses in ANPPsensitivity to chronic alterations in water availability within an ecosystem may not conform to regional AP-ANPP patterns, despite expected changes in ANPP and plant communities. The result is unanticipated functional resistance to climate change at the site scale.

1 aWilcox, K.R.1 aBlair, John, M.1 aSmith, M.D.1 aKnapp, Alan, K. uhttps://esajournals.onlinelibrary.wiley.com/doi/full/10.1890/15-1437.102713nas a2200241 4500008004100000245014200041210006900183300001200252490000700264520191200271653002102183653001702204653003002221653001402251653002602265653001702291100002802308700002102336700001602357700001602373700001602389856006602405 2016 eng d00aDrivers of variation in aboveground net primary productivity and plant community composition differ across a broad precipitation gradient0 aDrivers of variation in aboveground net primary productivity and a521-5330 v193 a

Aboveground net primary production (ANPP) is a key integrator of C uptake and energy flow in many terrestrial ecosystems. As such, ecologists have long sought to understand the factors driving variation in this important ecosystem process. Although total annual precipitation has been shown to be a strong predictor of ANPP in grasslands across broad spatial scales, it is often a poor predictor at local scales. Here we examine the amount of variation in ANPP that can be explained by total annual precipitation versus precipitation during specific periods of the year (precipitation periods) and nutrient availability at three sites representing the major grassland types (shortgrass steppe, mixed-grass prairie, and tallgrass prairie) spanning the broad precipitation gradient of the U.S. Central Great Plains. Using observational data, we found that precipitation periods and nutrient availability were much stronger predictors of site-level ANPP than total annual precipitation. However, the specific nutrients and precipitation periods that best predicted ANPP differed among the three sites. These effects were mirrored experimentally at the shortgrass and tallgrass sites, with precipitation and nutrient availability co-limiting ANPP, but not at the mixed-grass site, where nutrient availability determined ANPP exclusive of precipitation effects. Dominant grasses drove the ANPP response to increased nutrient availability at all three sites. However, the relative responses of rare grasses and forbs were greater than those of the dominant grasses to experimental nutrient additions, thus potentially driving species turnover with chronic nutrient additions. This improved understanding of the factors driving variation in ANPP within ecosystems spanning the broad precipitation gradient of the Great Plains will aid predictions of alterations in ANPP under future global change scenarios.

10adominant species10aGreat Plains10aNutrient Network (NutNet)10anutrients10aprecipitation periods10arare species1 aLa Pierre, Kimberly, J.1 aBlumenthal, D.M.1 aBrown, C.S.1 aKlein, J.A.1 aSmith, M.D. uhttps://link.springer.com/article/10.1007%2Fs10021-015-9949-702250nas a2200193 4500008004100000245008700041210006900128300001400197490000800211520160600219653004101825653002401866653001801890653002501908653002201933100001901955700001601974856006601990 2016 eng d00aThe effect of timing of growing season drought on flowering of a dominant C4 grass0 aeffect of timing of growing season drought on flowering of a dom a391 - 3990 v1813 a

Timing of precipitation is equally important as amount for determining ecosystem function, especially aboveground net primary productivity (ANPP), in a number of ecosystems. In tallgrass prairie of the Central Plains of North America, grass flowering stalks of dominant C4 grasses, such as Andropogon gerardii, can account for more than 70 % of ANPP, or almost none of it, as the number of flowering stalks produced is highly variable. Although growing season precipitation amount is important for driving variation in flowering stalk production, it remains unknown whether there are critical periods within the growing season in which sufficient rainfall must occur to allow for flowering. The effect of timing of rainfall deficit (drought) on flowering of A. gerardii, was tested by excluding rainfall during three periods within the growing season (starting in mid-April, mid-May and mid-June). Mid-summer drought (starting in mid-June) strongly reduced the flowering rate (e.g., density and biomass) of A. gerardii (e.g., as high as 94 % compared to the control), suggesting flowering is highly sensitive to precipitation at this time. This effect appeared to be related to plant water status at the time of flowering stalk initiation, rather than an indirect consequence of reduced C assimilation. Our results suggest that increased frequency of growing season drought forecast with climate change could reduce sexual reproduction in this dominant grass species, particularly if it coincides with timing of flowering stalk initiation, with important implications for ecosystem functioning.

10aAboveground net primary productivity10aAndropogon gerardii10aEcophysiology10aPrecipitation timing10atallgrass prairie1 aDietrich, J.D.1 aSmith, M.D. uhttps://link.springer.com/article/10.1007%2Fs00442-016-3579-401867nas a2200145 4500008004100000245012700041210006900168300001000237490000600247520137100253100001601624700001801640700001701658856004601675 2016 eng d00aGene expression patterns of two dominant tallgrass prairie species differ in response to warming and altered precipitation0 aGene expression patterns of two dominant tallgrass prairie speci a255220 v63 a

To better understand the mechanisms underlying plant species responses to climate change, we compared transcriptional profiles of the co-dominant C4 grasses, Andropogon gerardii Vitman and Sorghastrum nutans (L.) Nash, in response to increased temperatures and more variable precipitation regimes in a long-term field experiment in native tallgrass prairie. We used microarray probing of a closely related model species (Zea mays) to assess correlations in leaf temperature (Tleaf) and leaf water potential (LWP) and abundance changes of ~10,000 transcripts in leaf tissue collected from individuals of both species. A greater number of transcripts were found to significantly change in abundance levels with Tleaf and LWP in S. nutans than in A. gerardii. S. nutans also was more responsive to short-term drought recovery than A. gerardii. Water flow regulating transcripts associated with stress avoidance (e.g., aquaporins), as well as those involved in the prevention and repair of damage (e.g., antioxidant enzymes, HSPs), were uniquely more abundant in response to increasing Tleaf in S. nutans. The differential transcriptomic responses of the co-dominant C4 grasses suggest that these species may cope with and respond to temperature and water stress at the molecular level in distinct ways, with implications for tallgrass prairie ecosystem function.

1 aSmith, M.D.1 aHoffman, A.M.1 aAvolio, M.L. uhttps://www.nature.com/articles/srep2552202183nas a2200145 4500008004100000245010100041210006900142300001600211490000800227520167500235100001701910700002001927700001601947856007401963 2016 eng d00aThe immediate and prolonged effects of climate extremes on soil respiration in a mesic grassland0 aimmediate and prolonged effects of climate extremes on soil resp a1034 - 10440 v1213 a

The predicted increase in the frequency and intensity of climate extremes is expected to impact terrestrial carbon fluxes to the atmosphere, potentially changing ecosystems from carbon sinks to sources, with positive feedbacks to climate change. As the second largest terrestrial carbon flux, soil CO2 efflux or soil respiration (Rs) is strongly influenced by soil temperature and moisture. Thus, climate extremes such as heat waves and extreme drought should have substantial impacts on Rs. We investigated the effects of such climate extremes on growing season Rs in a mesic grassland by experimentally imposing 2 years of extreme drought combined with midsummer heat waves. After this 2 year period, we continued to measure Rs during a recovery year. Two consecutive drought years reduced Rs by about 25% each growing season; however, when normal rainfall returned during the recovery year, formerly droughted plots had higher rates of Rs than control plots (up to +17%). The heat wave treatments had no effect on Rs, alone or when combined with drought, and during the growing season, soil moisture was the primary driver of Rs with little evidence for Rs temperature sensitivity. When compared to aboveground net primary production, growing season Rs was much less sensitive to drought but was more responsive postdrought. These results are consistent with the hypothesis that ecosystems become sources of CO2 during drought because carbon inputs (production) are decreased relatively more than outputs (respiration). Moreover, stimulation of Rs postdrought may lengthen the time required for net carbon exchange to return to predrought levels.

1 aHoover, D.L.1 aKnapp, Alan, K.1 aSmith, M.D. uhttps://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015JG00325602529nas a2200421 4500008004100000245009300041210006900134300001400203490000800217520139200225100001601617700001901633700001901652700001601671700001401687700001801701700001601719700001901735700001501754700001601769700001701785700001801802700001801820700001901838700001701857700001401874700001301888700001701901700001501918700001801933700002101951700002001972700001701992700001702009700001702026700001602043856004802059 2016 eng d00aIntegrative modelling reveals mechanisms linking productivity and plant species richness0 aIntegrative modelling reveals mechanisms linking productivity an a390 - 3930 v5293 a

How ecosystem productivity and species richness are interrelated is one of the most debated subjects in the history of ecology1. Decades of intensive study have yet to discern the actual mechanisms behind observed global patterns2, 3. Here, by integrating the predictions from multiple theories into a single model and using data from 1,126 grassland plots spanning five continents, we detect the clear signals of numerous underlying mechanisms linking productivity and richness. We find that an integrative model has substantially higher explanatory power than traditional bivariate analyses. In addition, the specific results unveil several surprising findings that conflict with classical models4, 5, 6, 7. These include the isolation of a strong and consistent enhancement of productivity by richness, an effect in striking contrast with superficial data patterns. Also revealed is a consistent importance of competition across the full range of productivity values, in direct conflict with some (but not all) proposed models. The promotion of local richness by macroecological gradients in climatic favourability, generally seen as a competing hypothesis8, is also found to be important in our analysis. The results demonstrate that an integrative modelling approach leads to a major advance in our ability to discern the underlying processes operating in ecological systems.

1 aGrace, J.B.1 aAnderson, T.M.1 aSeabloom, E.W.1 aBorer, E.T.1 aAdler, P.1 aHarpole, W.S.1 aHautier, Y.1 aHillebrand, H.1 aLind, E.M.1 aPärtel, M.1 aBakker, J.D.1 aBuckley, Y.M.1 aCrawley, M.J.1 aDamschen, E.I.1 aDavies, K.F.1 aFay, P.A.1 aFirn, J.1 aGruner, D.S.1 aHector, A.1 aKnops, J.M.H.1 aMacDougall, A.S.1 aMelbourne, B.A.1 aMorgan, J.W.1 aOrrock, J.L.1 aProber, S.M.1 aSmith, M.D. uhttps://www.nature.com/articles/nature1652403182nas a2200181 4500008004100000245012000041210006900161300001400230490000800244520254700252100001802799700001702817700002802834700001702862700001602879700002402895856008102919 2016 eng d00aNutrient additions cause divergence of tallgrass prairie plant communities resulting in loss of ecosystem stability0 aNutrient additions cause divergence of tallgrass prairie plant c a1478-14870 v1043 a

1.Nitrogen (N) and phosphorus (P) deposition due to pollution and land-use change are dramatically altering biogeochemical cycles. These altered nutrient inputs affect plant communities by generally increasing dominance and reducing diversity, as well as altering community variability (heterogeneity). Less well studied are effects of changes in community variability on ecosystem functions, such as productivity, or the stability of those functions. 2.Here we use a twelve-year nutrient addition experiment in tallgrass prairie to determine variability in community responses to N and P additions and link these responses to ecosystem productivity and stability. We added two levels of N and four levels of P in a fully factorial design to 25-m2 plots in native tallgrass prairie in northeastern Kansas, USA. Each year percent cover of each species was measured in June and August in a 1-m2 subplot of each plot, and annual net primary productivity was measured in two 0.1-m2 subplots in each plot at the end of each growing season. 3.The addition of N and P together increased plant community variability across space (i.e., the replicates were significantly more different from each other in the N + P treatments than they were in the control treatment). We also found that variability of the plant community within a single plot through time increased with the addition of N alone and N and P together. The highest level of both spatial and temporal variability occurred in plots with the highest level of nutrient addition (10 g m−2 of both N and P). 4.While we found no linkage between spatial variability of community composition and the spatial stability of productivity, the temporal stability of productivity decreased with increasing temporal plant community variability. Additionally, the ability to predict the productivity response to growing season precipitation, a key environmental variable, also decreased under higher temporal community variability. 5.Synthesis. Using a 12-yr nutrient addition experiment, we found that nutrient addition leads to both spatial and temporal community variability in mesic tallgrass prairie. The changes in community variability through time were directly related to ecosystem stability. While overall shifts in community structure in response to nutrient additions are important, the change in variability of local communities has significant implications for our ability to predict how patterns of biodiversity and ecosystem function will respond to a rapidly changing world.

1 aKoerner, S.E.1 aAvolio, M.L.1 aLa Pierre, Kimberly, J.1 aWilcox, K.R.1 aSmith, M.D.1 aCollins, Scott., L. uhttps://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2745.1261000681nas a2200241 4500008004100000245006800041210006800109300001200177490000700189653001200196653001400208653001200222653001400234653002500248653001300273100002000286700002000306700001400326700001600340700001700356700001700373856004900390 2016 eng d00aRangeland responses to predicted increases in drought extremity0 aRangeland responses to predicted increases in drought extremity a191-1960 v3810aDrought10agrassland10asavanna10ashrubland10astate and transition10awoodland1 aBreshears, D.D.1 aKnapp, Alan, K.1 aLaw, D.J.1 aSmith, M.D.1 aTwidwell, D.1 aWonkka, C.L. uhttp://dx.doi.org/10.1016/j.rala.2016.06.00902102nas a2200361 4500008004100000245011900041210006900160300001400229490000700243520104200250653004101292653000901333653001401342653001201356653002001368100001601388700002001404700002401424700002001448700001801468700001801486700001901504700002001523700001601543700001201559700002001571700001701591700001701608700001601625700001701641700001701658856006501675 2016 eng d00aShared drivers but divergent ecological responses: Insights from long-term experiments in mesic savanna grasslands0 aShared drivers but divergent ecological responses Insights from  a666 - 6820 v663 a

Fire and grazing, key determinants of structure and function of savanna grasslands worldwide, have been extensively altered by humans. We used existing long-term manipulations of fire and grazing in North American and South African mesic savanna grasslands, as well as new experiments, to determine whether the impacts of fire and grazing by large herbivores differed between these systems. We found that despite a body of literature suggesting that these savanna grasslands respond uniquely to fire and grazing, their ecosystem responses (aboveground productivity) were generally similar. In contrast, plant-community responses to fire and herbivores diverged strongly between systems. The differences in plant-community responses, as well as convergence in ecosystem function, were underpinned by a common mechanism: the response of grass dominance to changing fire and grazing regimes. As a result, divergent responses of plant communities to altered fire and grazing regimes did not preclude convergence in ecosystem function.

10aAboveground net primary productivity10afire10agrassland10aGrazing10aplant community1 aSmith, M.D.1 aKnapp, Alan, K.1 aCollins, Scott., L.1 aBurkepile, D.E.1 aKirkman, K.P.1 aKoerner, S.E.1 aThompson, D.I.1 aBlair, John, M.1 aBurns, C.E.1 aEby, S.1 aForrestel, E.J.1 aFynn, R.W.S.1 aGovender, N.1 aHagenah, N.1 aHoover, D.L.1 aWilcox, K.R. uhttps://academic.oup.com/bioscience/article/66/8/666/246414102500nas a2200193 4500008004100000245012200041210006900163300001300232490000800245520183900253653001902092653001302111653003002124653001502154653002702169100002802196700001602224856006602240 2016 eng d00aSoil nutrient additions increase invertebrate herbivore abundances, but not herbivory, across three grassland systems0 aSoil nutrient additions increase invertebrate herbivore abundanc a485 -4970 v1803 a

Resource availability may influence invertebrate communities, with important consequences for ecosystem function, such as biomass production. We assessed: (1) the effects of experimental soil nutrient additions on invertebrate abundances and feeding rates and (2) the resultant changes in the effects of invertebrates on aboveground plant biomass at three grassland sites spanning the North American Central Plains, across which plant tissue chemistry and biomass vary. Invertebrate communities and rates of herbivory were sampled within a long-term nutrient-addition experiment established at each site along the broad Central Plains precipitation gradient. Additionally, the effects of invertebrates on aboveground plant biomass were determined under ambient and elevated nutrient conditions. At the more mesic sites, invertebrate herbivore abundances increased and their per capita rate of herbivory decreased with nutrient additions. In contrast, at the semi-arid site where plant biomass is low and plant nutrient concentrations are high, invertebrate herbivore abundances did not vary and per capita rates of herbivory increased with nutrient additions. No change in the effect of invertebrate herbivores on aboveground plant biomass was observed at any of the sites. In sum, nutrient additions induced shifts in both plant biomass and leaf nutrient content, which altered invertebrate abundances and feeding rate. However, due to the inverse relationship between changes in herbivore abundance and per capita rates of herbivory, nutrient additions did not alter the effect of invertebrates on aboveground biomass. Overall, we suggest that this inverse response of herbivore abundance and per capita feeding rate may buffer ecosystems against changes in invertebrate damage in response to fluctuations in nutrient levels.

10aCentral Plains10anitrogen10aPer capita herbivory rate10aPhosphorus10aPlant tissue chemistry1 aLa Pierre, Kimberly, J.1 aSmith, M.D. uhttps://link.springer.com/article/10.1007%2Fs00442-015-3471-702723nas a2200241 4500008004100000245013000041210006900171300001500240490000700255520196000262653002202222100002002244700001702264700001702281700001702298700001802315700002802333700001502361700001202376700001502388700001602403856006202419 2015 eng d00aCharacterizing differences in precipitation regimes of extreme wet and dry years: Implications for climate change experiments0 aCharacterizing differences in precipitation regimes of extreme w a2624 -26330 v213 a

Climate change is intensifying the hydrologic cycle and is expected to increase the frequency of extreme wet and dry years. Beyond precipitation amount, extreme wet and dry years may differ in other ways, such as the number of precipitation events, event size, and the time between events. We assessed 1614 long-term (100 year) precipitation records from around the world to identify key attributes of precipitation regimes, besides amount, that distinguish statistically extreme wet from extreme dry years. In general, in regions where mean annual precipitation (MAP) exceeded 1000 mm, precipitation amounts in extreme wet and dry years differed from average years by ~40% and 30%, respectively. The magnitude of these deviations increased to >60% for dry years and to >150% for wet years in arid regions (MAP<500 mm). Extreme wet years were primarily distinguished from average and extreme dry years by the presence of multiple extreme (large) daily precipitation events (events >99th percentile of all events); these occurred twice as often in extreme wet years compared to average years. In contrast, these large precipitation events were rare in extreme dry years. Less important for distinguishing extreme wet from dry years were mean event size and frequency, or the number of dry days between events. However, extreme dry years were distinguished from average years by an increase in the number of dry days between events. These precipitation regime attributes consistently differed between extreme wet and dry years across 12 major terrestrial ecoregions from around the world, from deserts to the tropics. Thus, we recommend that climate change experiments and model simulations incorporate these differences in key precipitation regime attributes, as well as amount into treatments. This will allow experiments to more realistically simulate extreme precipitation years and more accurately assess the ecological consequences.

10arainfall patterns1 aKnapp, Alan, K.1 aHoover, D.L.1 aWilcox, K.R.1 aAvolio, M.L.1 aKoerner, S.E.1 aLa Pierre, Kimberly, J.1 aLoik, M.E.1 aLuo, Y.1 aSala, O.E.1 aSmith, M.D. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.1288802530nas a2200241 4500008004100000245008400041210006900125300001300194490000800207520176300215653001901978653002501997653003402022653001802056653002302074100002002097700002002117700001702137700002802154700002402182700001602206856006602222 2015 eng d00aDifferential sensitivity to regional-scale drought in six central US grasslands0 aDifferential sensitivity to regionalscale drought in six central a949 -9570 v1773 a

Terrestrial ecosystems often vary dramatically in their responses to drought, but the reasons for this are unclear. With climate change forecasts for more frequent and extensive drought in the future, a more complete understanding of the mechanisms that determine differential ecosystem sensitivity to drought is needed. In 2012, the Central US experienced the fourth largest drought in a century, with a regional-scale 40 % reduction in growing season precipitation affecting ecosystems ranging from desert grassland to mesic tallgrass prairie. This provided an opportunity to assess ecosystem sensitivity to a drought of common magnitude in six native grasslands. We tested the prediction that drought sensitivity is inversely related to mean annual precipitation (MAP) by quantifying reductions in aboveground net primary production (ANPP). Long-term ANPP data available for each site (mean length = 16 years) were used as a baseline for calculating reductions in ANPP, and drought sensitivity was estimated as the reduction in ANPP per millimeter reduction in precipitation. Arid grasslands were the most sensitive to drought, but drought responses and sensitivity varied by more than twofold among the six grasslands, despite all sites experiencing 40 % reductions in growing season precipitation. Although drought sensitivity generally decreased with increasing MAP as predicted, there was evidence that the identity and traits of the dominant species, as well as plant functional diversity, influenced sensitivity. A more comprehensive understanding of the mechanisms leading to differences in drought sensitivity will require multi-site manipulative experiments designed to assess both biotic and abiotic determinants of ecosystem sensitivity.

10aClimate change10aFunctional diversity10aLong-term ecological research10aPrecipitation10aPrimary production1 aKnapp, Alan, K.1 aCarroll, C.J.W.1 aDenton, E.M.1 aLa Pierre, Kimberly, J.1 aCollins, Scott., L.1 aSmith, M.D. uhttps://link.springer.com/article/10.1007%2Fs00442-015-3233-602569nas a2200265 4500008004100000245012600041210006900167300001100236490000600247520170500253653002301958653003601981653002002017653002102037653002602058653002302084653002402107653001702131653002202148100001702170700001602187700001502203700001602218856006902234 2015 eng d00aThe effects of genotype richness and genomic dissimilarity of Andropogon gerardii on invasion resistance and productivity0 aeffects of genotype richness and genomic dissimilarity of Androp a61 -710 v83 a

Background: The genetic diversity within populations has been shown to affect ecosystem functions, including productivity and invasion resistance. To date most experiments have focused on manipulation of genotypic richness and have ignored other measures of genetic diversity. Aims: In the present study we aimed to establish whether manipulated genotypic richness and genomic dissimilarity of Andropogon gerardii affect productivity and invasion resistance. Methods: We created experimental mesocosms with three levels of genotypic richness: one-, three-, and nine-genotypes. In the three-genotype treatment, we manipulated a range of genomic dissimilarity values (genetic relatedness among individuals). At the end of one growing season we measured above-ground, below-ground and total biomass of the mesocosms, and invasion resistance to Andropogon bladhii. Results: Overall, we found no significant effect of genotypic richness on any measure of ecosystem function, although there tended to be more root biomass (due to complementarity) and invasive seedling biomass with higher levels of genotypic richness. Within the three-genotype treatment we found a significant positive relationship between genomic dissimilarity and above-ground biomass, which was caused by a selection effect. We also found a positive relationship between genomic dissimilarity and biomass of A. bladhii. Conclusions: Using these two measures of genetic diversity we detected differences in the strength and mechanism of positive diversity effects within the same experiment, demonstrating the value of manipulating multiple measures of diversity when performing biodiversity–ecosystem function experiments.

10aAndropogon bladhii10abiodiversity ecosystem function10acomplementarity10adominant species10agenomic dissimilarity10agenotypic richness10ainvasion resistance10aproductivity10atallgrass prairie1 aAvolio, M.L.1 aChang, C.C.1 aWeis, J.J.1 aSmith, M.D. uhttps://www.tandfonline.com/doi/abs/10.1080/17550874.2013.86699002932nas a2200157 4500008004100000245016400041210006900205300001300274490000800287520232900295653001402624100002002638700001902658700001602677856008102693 2015 eng d00aFunctional differences between dominant grasses drive divergent responses to large herbivore loss in mesic savanna grasslands of North America and South Africa0 aFunctional differences between dominant grasses drive divergent  a714 -7240 v1033 a

Grazing and fire are disturbances integral to the evolution and maintenance of savanna grasslands. Humans are altering or completely eliminating these disturbance regimes at a global scale, with important consequences for savanna ecosystem structure and function. It is unknown whether the alteration of these disturbance regimes will have similar effects on grass communities of savanna grasslands in different geographic regions that vary in their biogeographic and evolutionary histories, as well as in the diversity of extant grazers. Here, we examined the effects of large herbivore loss on different aspects of grass community structure – taxonomic, phylogenetic and functional – across a range of fire frequencies in C4-dominated mesic savanna grassland sites of North America (Konza Prairie Biological Station, Kansas, USA) and South Africa (Kruger National Park). The goal of the study was to determine whether the loss of large herbivores exerted a consistent effect on the grass communities of two physiognomically similar grasslands with different biogeographic and grazing histories. The removal of large herbivores resulted in divergent responses in the grass communities at Konza and Kruger that was consistent across fire treatments. At Konza, there was a rapid and significant response to grazing exclusion while the response was muted and transient at Kruger. Functional syndromes associated with grazing resistance were generally conserved across sites, and it was the functional strategies of the dominant species at each site that drove the divergent responses. Further, our study supports the hypothesis that grazing and aridity may be selective forces that act in parallel as those species that were grazing resistant also occupied drier niches. Synthesis. Our study demonstrates that savanna grassland communities with different biogeographic and grazing histories respond differently to the removal of large herbivores and that climate, fire and grazing are interactive forces in maintaining savanna grassland diversity and function. We show that the functional attributes of the dominant grasses, which are in part driven by the biogeographic and grazing history experienced, are the most relevant in predicting the response of savanna ecosystems to the loss of large herbivores.

10aphylogeny1 aForrestel, E.J.1 aDonoghue, M.J.1 aSmith, M.D. uhttps://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2745.1237602294nas a2200205 4500008004100000245010400041210006900145300001300214490000800227520162100235653002101856653001701877653002101894653002201915653001901937653002201956100002801978700001602006856006602022 2015 eng d00aFunctional trait expression of grassland species shift with short- and long-term nutrient additions0 aFunctional trait expression of grassland species shift with shor a307 -3180 v2163 a

Humans are altering nutrient availability worldwide, likely affecting plant trait expression, with consequences for community composition and ecosystem function. Here, we examined the responses of plant species dominant under ambient nutrient conditions (baseline species) versus those that become dominant under increased nutrient conditions (enriched species) in a tallgrass prairie ecosystem. The expression of 8 functional traits was quantified for 3 baseline and 3 enriched species within one short-term and one long-term nutrient addition experiment. We found that enriched species occupied a trait space characterized by traits that generally correspond with faster growth rates than baseline species. Additionally, the enriched species shifted in their trait expression relative to the control more than the baseline species with nutrient additions, particularly within the long-term experiment. The trait space shifts of individual species with nutrient additions scaled up to affect community aggregate trait values within both experiments. However, traits that responded to nutrient additions at the community level were not strong predictors of aboveground net primary productivity (ANPP) within the short-term experiment. In contrast, in the long-term experiment, one response trait (community aggregate height) strongly correlated with variation in ANPP with nutrient additions. The link between plant functional traits and community and ecosystem responses to chronic nutrient additions shown here will provide important insight into key mechanisms driving grassland responses to global change.

10aBaseline species10aEffect trait10aEnriched species10aNutrient addition10aResponse trait10atallgrass prairie1 aLa Pierre, Kimberly, J.1 aSmith, M.D. uhttps://link.springer.com/article/10.1007%2Fs11258-014-0438-402791nas a2200337 4500008004100000022001400041245013400055210006900189260001600258300001400274490000800288520170200296653002901998653004202027653004902069653002202118653003102140100001602171700002802187700002402215700002002239700001602259700001802275700001502293700001402308700001702322700001702339700001702356700001402373856006602387 2015 eng d a0029-854900aGlobal environmental change and the nature of aboveground net primary productivity responses: insights from long-term experiments0 aGlobal environmental change and the nature of aboveground net pr cJan-04-2015 a935 - 9470 v1773 a

Many global change drivers chronically alter resource availability in terrestrial ecosystems. Such resource alterations are known to affect aboveground net primary production (ANPP) in the short term; however, it is unknown if patterns of response change through time. We examined the magnitude, direction, and pattern of ANPP responses to a wide range of global change drivers by compiling 73 datasets from long-term (>5 years) experiments that varied by ecosystem type, length of manipulation, and the type of manipulation. Chronic resource alterations resulted in a significant change in ANPP irrespective of ecosystem type, the length of the experiment, and the resource manipulated. However, the pattern of ecosystem response over time varied with ecosystem type and manipulation length. Continuous directional responses were the most common pattern observed in herbaceous-dominated ecosystems. Continuous directional responses also were frequently observed in longer-term experiments (>11 years) and were, in some cases, accompanied by large shifts in community composition. In contrast, stepped responses were common in forests and other ecosystems (salt marshes and dry valleys) and with nutrient manipulations. Our results suggest that the response of ANPP to chronic resource manipulations can be quite variable; however, responses persist once they occur, as few transient responses were observed. Shifts in plant community composition over time could be important determinants of patterns of terrestrial ecosystem sensitivity, but comparative, long-term studies are required to understand how and why ecosystems differ in their sensitivity to chronic resource alterations.

10aAboveground productivity10aHierarchical response framework (HRF)10aLong-Term Ecological Research (LTER) Network10aNutrient addition10aPrecipitation manipulation1 aSmith, M.D.1 aLa Pierre, Kimberly, J.1 aCollins, Scott., L.1 aKnapp, Alan, K.1 aGross, K.L.1 aBarrett, J.E.1 aFrey, S.D.1 aGough, L.1 aMiller, R.J.1 aMorris, J.T.1 aRustad, L.E.1 aYarie, J. uhttps://link.springer.com/article/10.1007%2Fs00442-015-3230-902306nas a2200181 4500008004100000245008900041210006900130300001600199490000800215520172300223100001801946700001701964700001601981700001301997700001702010700001602027856008102043 2015 eng d00aInvasibility of a mesic grassland depends on the time-scale of fluctuating resources0 aInvasibility of a mesic grassland depends on the timescale of fl a1538 - 15460 v1033 a

1. Global change is increasing the frequency and magnitude of resource fluctuations (pulses) at multiple time-scales. According to the fluctuating resource availability hypothesis (FRAH), susceptibility of an ecosystem to invasion (i.e. invasibility) is expected to increase whenever resource supply exceeds that which is utilized by native communities. Thus, global change has the potential to increase invasibility around the world. 2. Here, we test the FRAH by adding seeds of a target invader grass species to a long-term climate change experiment manipulating precipitation pulse size in tallgrass prairie in Kansas, USA. 3. Our experimental work yielded three important findings. First, contrary to predictions of the FRAH, invasibility was reduced with short time-scale resource pulses (intra-annual time-scale). Secondly, we found evidence to suggest that at inter-annual time-scales, the FRAH is supported. Wet years resulted in an increase in the number of established seedlings as well as the number of seedlings that persisted to the end of the season. Finally, we found that invasibility was positively related to native community richness and the density of individuals in the community suggesting that native communities facilitate establishment of invader species. Perhaps more importantly, results from this 10-year invasion study also show that resource availability drives invasion and that the biotic filters of plant community structure and diversity are secondary. 4. Synthesis. Our findings suggest that intensification of precipitation regimes may enhance resistance to invasion at intra-annual time-scales, but will have opposing effects if precipitation regimes include more wet years.

1 aKoerner, S.E.1 aAvolio, M.L.1 aChang, C.C.1 aGrey, J.1 aHoover, D.L.1 aSmith, M.D. uhttps://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2745.1247902172nas a2200145 4500008004100000245015400041210006900195300001300264490000800277520161600285100002801901700001901929700001601948856006201964 2015 eng d00aInvertebrate, not small vertebrate, herbivory interacts with nutrient availability to impact tallgrass prairie community composition and forb biomass0 aInvertebrate not small vertebrate herbivory interacts with nutri a842 -8500 v1243 a

The effects of herbivores and their interactions with nutrient availability on primary production and plant community composition in grassland systems is expected to vary with herbivore type. We examined the effects of invertebrate and small vertebrate herbivores and their interactions with nutrient availability on grassland plant community composition and aboveground biomass in a tallgrass prairie ecosystem. The abundance of forbs relative to grasses increased with invertebrate herbivore removals. This increase in forb abundance led to a shift in community composition, where invertebrate removals resulted in greater plant species evenness as well as a divergence in composition among plots. In contrast, vertebrate herbivore removals did not affect plant community composition or aboveground biomass. Nutrient additions alone resulted in a decrease in plant species richness and an increase in the abundance of the dominant grass, but the dominant grass species did not greatly increase in abundance when nutrient additions were combined with invertebrate removals. Rather, several subdominant forbs came to dominate the plant community. Additionally, the combined nutrient addition and invertebrate herbivore removal treatment increased forb biomass, suggesting that invertebrate herbivores suppress the responses of forb species to chronic nutrient additions. Overall, the release of forbs from invertebrate herbivore pressure may result in large shifts in species composition, with consequences for aboveground biomass and forage quality due to altered grass:forb ratios in grassland systems.

1 aLa Pierre, Kimberly, J.1 aJoern, Anthony1 aSmith, M.D. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/oik.0186901709nas a2200193 4500008004100000245011500041210006900156260001200225300000900237490000700246520108400253100001101337700001701348700002801365700002001393700001201413700001601425856007401441 2015 eng d00aStoichiometric homeostasis predicts plant species dominance, temporal stability and responses to global change0 aStoichiometric homeostasis predicts plant species dominance temp c09/2015 a23350 v963 a

Why some species are consistently more abundant than others, and predicting how species will respond to global change, are fundamental questions in ecology. Long-term observations indicate that plant species with high stoichiometric homeostasis for nitrogen (HN), i.e., the ability to decouple foliar N levels from variation in soil N availability, were more common and stable through time than low HN species in a central US grassland. However, with 9-yrs of nitrogen addition, species with high HN decreased in abundance, while those with low HN increased in abundance. In contrast, in climate change experiments simulating a range of forecast hydrologic changes - extreme drought (2-yrs), increased rainfall variability (14-yrs), and chronic increases in rainfall (21-yrs) - plant species with the highest HN were least responsive to changes in soil water availability. These results suggest that HN may be predictive of plant species success and stability, and how plant species and ecosystems will respond to global-change driven alterations in resource availability.

1 aYu, Q.1 aWilcox, K.R.1 aLa Pierre, Kimberly, J.1 aKnapp, Alan, K.1 aHan, X.1 aSmith, M.D. uhttps://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/14-1897.102883nas a2200193 4500008004100000245016700041210006900208300001500277490000800292520217100300100001702471700001802488700002802506700001702534700001702551700001602568700002402584856008102608 2014 eng d00aChanges in plant community composition, not diversity, during a decade of nitrogen and phosphorus additions drive above-ground productivity in a tallgrass prairie0 aChanges in plant community composition not diversity during a de a1649 -16600 v1023 a

Nutrient additions typically increase terrestrial ecosystem productivity, reduce plant diversity and alter plant community composition; however, the effects of P additions and interactions between N and P are understudied. We added both N (10 g m−2) and three levels of P (2.5, 5 and 10 g m−2) to a native, ungrazed tallgrass prairie burned biennially in northeastern Kansas, USA, to determine the independent and interactive effects of N and P on plant community composition and above-ground net primary productivity (ANPP). After a decade of nutrient additions, we found few effects of P alone on plant community composition, N alone had stronger effects, and N and P additions combined resulted in much larger effects than either alone. The changes in the plant community were driven by decreased abundance of C4 grasses, perhaps in response to altered interactions with mycorrhizal fungi, concurrent with increased abundance of non-N-fixing perennial and annual forbs. Surprisingly, this large shift in plant community composition had little effect on plant community richness, evenness and diversity. The shift in plant composition with N and P combined had large but variable effects on ANPP over time. Initially, N and N and P combined increased above-ground productivity of C4 grasses, but after 4 years, productivity returned to ambient levels as grasses declined in abundance and the community shifted to dominance by non-N-fixing and annual forbs. Once these forbs increased in abundance and became dominant, ANPP was more variable, with pulses in forb production only in years when the site was burned. Synthesis. We found that a decade of N and P additions interacted to drive changes in plant community composition, which had large effects on ecosystem productivity but minimal effects on plant community diversity. The large shift in species composition increased variability in ANPP over time as a consequence of the effects of burning. Thus, increased inputs of N and P to terrestrial ecosystems have the potential to alter stability of ecosystem function over time, particularly within the context of natural disturbance regimes.

1 aAvolio, M.L.1 aKoerner, S.E.1 aLa Pierre, Kimberly, J.1 aWilcox, K.R.1 aWilson, G.T.1 aSmith, M.D.1 aCollins, Scott., L. uhttps://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2745.1231201969nas a2200193 4500008004100000245008300041210006900124300001300193490000800206520136600214653001901580653002101599653002001620653001901640653001701659100001701676700001601693856006601709 2014 eng d00aContrasting sensitivities of two dominant C4 grasses to heat waves and drought0 aContrasting sensitivities of two dominant C4 grasses to heat wav a721 -7310 v2153 a

Heat waves and droughts are predicted to increase in frequency and intensity with climate change. However, we lack a mechanistic understanding of the independent and interactive effects of severe heat and water stress for most ecosystems. In a mesic tallgrass prairie ecosystem, we used a factorial experimental approach to assess ecophysiological and productivity responses of two dominant C4 grasses, Andropogon gerardii and Sorghastrum nutans, to a season-long drought and a mid-summer heat wave at four intensities. We hypothesized that drought would have greater impacts than heat waves, that combined effects would be greater than either factor alone, and that the dominant grasses would differ in their responses to heat and water heat stress. We detected significant reductions in photosynthesis, leaf water potential, and productivity with drought but few direct responses to the heat waves. Surprisingly, there was no additive effect of heat and water stress on any plant response. However, S. nutans was more sensitive than A. gerardii to drought. In this grassland, water stress will likely dominate photosynthetic and productivity responses caused by discrete drought and heat wave events, rather than direct or additive effects of heat stress, with differential sensitivity in these grasses altering future ecosystem structure and function.

10aClimate change10aClimate extremes10aMesic grassland10aphotosynthesis10aproductivity1 aHoover, D.L.1 aSmith, M.D. uhttps://link.springer.com/article/10.1007%2Fs11258-014-0345-802006nas a2200145 4500008004100000245013900041210006900180300001500249490000800264520146600272100002001738700001901758700001601777856006701793 2014 eng d00aConvergent phylogenetic and functional responses to altered fire regimes in mesic savanna grasslands of North America and South Africa0 aConvergent phylogenetic and functional responses to altered fire a1000 -10110 v2033 a

The importance of fire in the creation and maintenance of mesic grassland communities is well recognized. Improved understanding of how grasses – the dominant clade in these important ecosystems – will respond to alterations in fire regimes is needed in the face of anthropogenically driven climate and land-use change. Here, we examined how grass communities shift in response to experimentally manipulated fire regimes at multiple levels of community diversity – taxonomic, phylogenetic and functional – in C4-dominanted mesic savanna grassland sites with similar structure and physiognomy, yet disparate biogeographic histories. We found that the grass communities were similar in their phylogenetic response and aspects of their functional response to high fire frequency. Both sites exhibited phylogenetic clustering of highly abundant species in annually burned plots, driven by species of the Andropogoneae, and a narrow range of functional strategies associated with rapid post-fire regeneration in a high-light, nitrogen-limited environment. By examining multiple facets of diversity in a comparative context, we identified convergent phylogenetic and functional responses to altered fire regimes in two mesic savanna grasslands. Our results highlight the importance of a common filtering process associated with fire that is consistent across grasslands of disparate biogeographic histories and taxonomic representation.

1 aForrestel, E.J.1 aDonoghue, M.J.1 aSmith, M.D. uhttps://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.1284602945nas a2200229 4500008004100000245010700041210006900148300001300217490000700230520226300237100001202500700001702512700001402529700001702543700001702560700002402577700001802601700001602619700002002635700001202655856004802667 2014 eng d00aDifferential effects of extreme drought on production and respiration: Synthesis and modeling analysis0 aDifferential effects of extreme drought on production and respir a621 -6330 v113 a

Extremes in climate may severely impact ecosystem structure and function, with both the magnitude and rate of response differing among ecosystem types and processes. We conducted a modeling analysis of the effects of extreme drought on two key ecosystem processes, production and respiration, and, to provide a broader context, we complemented this with a synthesis of published results that cover a wide variety of ecosystems. The synthesis indicated that across a broad range of biomes, gross primary production (GPP) was generally more sensitive to extreme drought (defined as proportional reduction relative to average rainfall periods) than was ecosystem respiration (ER). Furthermore, this differential sensitivity between production and respiration increased as drought severity increased; it occurred only in grassland ecosystems, and not in evergreen needle-leaf and broad-leaf forests or woody savannahs. The modeling analysis was designed to enable a better understanding of the mechanisms underlying this pattern, and focused on four grassland sites arrayed across the Great Plains, USA. Model results consistently showed that net primary productivity (NPP) was reduced more than heterotrophic respiration (Rh) by extreme drought (i.e., 67% reduction in annual ambient rainfall) at all four study sites. The sensitivity of NPP to drought was directly attributable to rainfall amount, whereas the sensitivity of Rh to drought was driven by soil drying, reduced carbon (C) input and a drought-induced reduction in soil C content – a much slower process. However, differences in reductions in NPP and Rh diminished as extreme drought continued, due to a gradual decline in the soil C pool leading to further reductions in Rh. We also varied the way in which drought was imposed in the modeling analysis; it was either imposed by simulating reductions in rainfall event size (ESR) or by reducing rainfall event number (REN). Modeled NPP and Rh decreased more by ESR than REN at the two relatively mesic sites but less so at the two xeric sites. Our findings suggest that responses of production and respiration differ in magnitude, occur on different timescales, and are affected by different mechanisms under extreme, prolonged drought.

1 aShi, Z.1 aThomey, M.L.1 aMowll, M.1 aLitvak, M.E.1 aBrunsell, N.1 aCollins, Scott., L.1 aPockman, W.T.1 aSmith, M.D.1 aKnapp, Alan, K.1 aLuo, Y. uhttps://www.biogeosciences.net/11/621/2014/02844nas a2200229 4500008004100000245015600041210006900197300001300266490000700279520203500286653002402321653001602345653002102361653001902382653002702401653001602428653004202444653003402486100001602520700001602536856006202552 2014 eng d00aDirect and indirect relationships between genetic diversity of a dominant grass, community diversity and above-ground productivity in tallgrass prairie0 aDirect and indirect relationships between genetic diversity of a a470 -4800 v253 a

Question Both genetic diversity within a dominant species and species diversity have been shown to affect productivity. However, these two levels of diversity have the potential to affect productivity in similar or opposing ways. Our study assessed direct and indirect relationships between genetic diversity of a dominant grass species and plant community diversity on productivity within a mesic grassland with naturally co-occurring genotypes and species. Location Konza Prairie Biological Station, Kansas, USA (39°05′35″ N, 96°33′31″ W). Methods We conducted a study at two sites (~65 plots per site) in intact tallgrass prairie that have been subjected to frequent (burned 14 times) and infrequent (burned nine times) fire treatments for ~30 yrs. With frequent burning, the dominant C4 grass, Andropogon gerardii, typically has higher abundance; in contrast, infrequently burned sites typically have higher species diversity but lower abundance of A. gerardii. Therefore, we hypothesized that genetic diversity within A. gerardii would have a significant direct relationship with productivity for the frequently burned site due to higher population abundances of A. gerardii overall, whereas species diversity would have a significant direct relationship with productivity for the infrequently burned site. Results Contrary to our predictions, genetic diversity of A. gerardii was not related to above-ground productivity either directly or indirectly via traits, while diversity at the community level had a negative indirect relationship with productivity via a negative effect of A. gerardii abundance on community diversity for both frequently and infrequently burned sites. Conclusions While much of the focus of diversity–productivity research has been on direct relationships between diversity at the community or population level separately, future studies should examine the indirect and potentially interactive effects of both levels of diversity in natural communities.

10aCommunity diversity10adisturbance10adominant species10aFire;Grassland10aPhylogenetic diversity10aPlant trait10aProductivity–diversity relationship10aStructural equation modelling1 aChang, C.C.1 aSmith, M.D. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/jvs.1210801982nas a2200757 4500008004100000245008400041210006900125300001400194490000800208100001600216700001900232700001700251700001700268700001900285700001500304700001400319700001600333700001900349700001700368700002000385700002100405700001600426700001800442700001800460700001600478700001200494700001800506700001800524700001400542700001900556700001700575700002000592700001100612700001300623700001600636700001800652700001500670700002400685700002000709700001600729700001800745700002800763700001900791700001100810700002100821700001900842700002000861700001900881700002200900700001800922700002100940700001700961700001600978700001700994700001501011700001401026700001601040700001601056700001801072700001901090700001901109700001601128700001701144700001501161856004801176 2014 eng d00aHerbivores and nutrients control grassland plant diversity via light limitation0 aHerbivores and nutrients control grassland plant diversity via l a517 - 5200 v5081 aBorer, E.T.1 aSeabloom, E.W.1 aGruner, D.S.1 aHarpole, W.S1 aHillebrand, H.1 aLind, E.M.1 aAdler, P.1 aAlberti, J.1 aAnderson, T.M.1 aBakker, J.D.1 aBiederman, L.A.1 aBlumenthal, D.M.1 aBrown, C.S.1 aBrudvig, L.A.1 aBuckley, Y.M.1 aCadotte, M.1 aChu, C.1 aCleland, E.E.1 aCrawley, M.J.1 aDaleo, P.1 aDamschen, E.I.1 aDavies, K.F.1 aDeCrappeo, N.M.1 aDu, G.1 aFirn, J.1 aHautier, Y.1 aHeckman, R.W.1 aHector, A.1 aHilleRisLambers, J.1 aIribarne, Oscar1 aKlein, J.A.1 aKnops, J.M.H.1 aLa Pierre, Kimberly, J.1 aLeakey, A.D.B.1 aLi, W.1 aMacDougall, A.S.1 aMcCulley, R.L.1 aMelbourne, B.A.1 aMitchell, C.E.1 aMoore, Joslin, L.1 aMortensen, B.1 aO'Halloran, L.R.1 aOrrock, J.L.1 aPascual, J.1 aProber, S.M.1 aPyke, D.A.1 aRisch, A.1 aSchuetz, M.1 aSmith, M.D.1 aStevens, C.J.1 aSullivan, L.L.1 aWilliams, R.J.1 aWragg, P.D.1 aWright, J.P.1 aYang, L.H. uhttps://www.nature.com/articles/nature1314402488nas a2200337 4500008004100000245011500041210006900156300001300225490000800238520150100246653001601747653000901763653001201772653002901784653002201813100001201835700002001847700001701867700001601884700001701900700001601917700001801933700001901951700001901970700001701989700002402006700001802030700002002048700001602068856006602084 2014 eng d00aLoss of a large grazer impacts savanna grassland plant communities similarly in North America and South Africa0 aLoss of a large grazer impacts savanna grassland plant communiti a293 -3030 v1753 a

Large herbivore grazing is a widespread disturbance in mesic savanna grasslands which increases herbaceous plant community richness and diversity. However, humans are modifying the impacts of grazing on these ecosystems by removing grazers. A more general understanding of how grazer loss will impact these ecosystems is hampered by differences in the diversity of large herbivore assemblages among savanna grasslands, which can affect the way that grazing influences plant communities. To avoid this we used two unique enclosures each containing a single, functionally similar large herbivore species. Specifically, we studied a bison (Bos bison) enclosure at Konza Prairie Biological Station, USA and an African buffalo (Syncerus caffer) enclosure in Kruger National Park, South Africa. Within these enclosures we erected exclosures in annually burned and unburned sites to determine how grazer loss would impact herbaceous plant communities, while controlling for potential fire-grazing interactions. At both sites, removal of the only grazer decreased grass and forb richness, evenness and diversity, over time. However, in Kruger these changes only occurred with burning. At both sites, changes in plant communities were driven by increased dominance with herbivore exclusion. At Konza, this was caused by increased abundance of one grass species, Andropogon gerardii, while at Kruger, three grasses, Themeda triandra, Panicum coloratum, and Digitaria eriantha increased in abundance.

10adisturbance10afire10aGrazing10aPlant community richness10aSpecies diversity1 aEby, S.1 aBurkepile, D.E.1 aFynn, R.W.S.1 aBurns, C.E.1 aGovender, N.1 aHagenah, N.1 aKoerner, S.E.1 aMatchett, K.J.1 aThompson, D.I.1 aWilcox, K.R.1 aCollins, Scott., L.1 aKirkman, K.P.1 aKnapp, Alan, K.1 aSmith, M.D. uhttps://link.springer.com/article/10.1007%2Fs00442-014-2895-902306nas a2200277 4500008004100000245012500041210006900166300001300235490000700248520144900255100001801704700002001722700001701742700001601759700001201775700001701787700001601804700001901820700001901839700001701858700002401875700001801899700002001917700001601937856007501953 2014 eng d00aPlant community response to loss of large herbivores differs between North American and South African savanna grasslands0 aPlant community response to loss of large herbivores differs bet a808 -8160 v953 a

Herbivory and fire shape plant community structure in grass-dominated ecosystems, but these disturbance regimes are being altered around the world. To assess the consequences of such alterations, we excluded large herbivores for seven years from mesic savanna grasslands sites burned at different frequencies in North America (Konza Prairie Biological Station, Kansas, USA) and South Africa (Kruger National Park). We hypothesized that the removal of a single grass-feeding herbivore from Konza would decrease plant community richness and shift community composition due to increased dominance by grasses. Similarly, we expected grass dominance to increase at Kruger when removing large herbivores, but because large herbivores are more diverse, targeting both grasses and forbs, at this study site, the changes due to herbivore removal would be muted. After seven years of large-herbivore exclusion, richness strongly decreased and community composition changed at Konza, whereas little change was evident at Kruger. We found that this divergence in response was largely due to differences in the traits and numbers of dominant grasses between the study sites rather than the predicted differences in herbivore assemblages. Thus, the diversity of large herbivores lost may be less important in determining plant community dynamics than the functional traits of the grasses that dominate mesic, disturbance-maintained savanna grasslands.

1 aKoerner, S.E.1 aBurkepile, D.E.1 aFynn, R.W.S.1 aBurns, C.E.1 aEby, S.1 aGovender, N.1 aHagenah, N.1 aMatchett, K.J.1 aThompson, D.I.1 aWilcox, K.R.1 aCollins, Scott., L.1 aKirkman, K.P.1 aKnapp, Alan, K.1 aSmith, M.D. uhttps://esajournals.onlinelibrary.wiley.com/doi/full/10.1890/13-1828.102943nas a2200277 4500008004100000245008900041210006900130300001100199490000700210520211800217653003402335653001902369653001302388653001602401653001402417653002902431653001002460653001802470653001702488100001802505700002402523700002002547700002002567700001602587856006202603 2014 eng d00aRainfall variability has minimal effects on grassland recovery from repeated grazing0 aRainfall variability has minimal effects on grassland recovery f a36 -440 v253 a

Question Mesic grasslands experience a complex disturbance regime including frequent fire, grazing by large ungulates and strong inter-annual climate variability. As a result of climate change, growing season precipitation regimes are predicted to become more variable, with larger event sizes and longer dry periods resulting in more temporally dynamic soil moisture regimes. Increased climate variability is likely to interact with other disturbances, such as grazing, in grassland ecosystems. We investigated the individual and combined effects of increased rainfall variability and grazing on plant community composition, structure and function in an annually burned, native tallgrass prairie. Our overarching question was: are grazing impacts modified under a more variable precipitation regime? Location Konza Prairie, Kansas, USA. Methods Plots were established within a long-term rainfall manipulation experiment in which larger, but less frequent, rain events were imposed during the growing season without altering the total rain amount. We then simulated intense grazing pressure during one growing season by repeatedly clipping all graminoids to 5 cm and monitored recovery over 3 yr. Results Neither grazing nor rainfall treatments affected species richness; however, grazing decreased total and grass above-ground net primary production (ANPP) and increased forb ANPP relative to ungrazed plots. Grass stem density recovered from intense grazing under ambient rainfall but did not fully recover, even after 2 yr in the altered rainfall treatment. Conclusions We found that increased rainfall variability had little effect on tallgrass prairie structure and function, while grazing had large effects. Grazing and increased rainfall variability interacted to suppress grass stem density and delayed recovery relative to controls. Although stem density was reduced, individual stem size increased, resulting in no net change in ANPP. This suggests that ANPP in grazed and ungrazed North American tallgrass prairie may be relatively resilient under more temporally variable precipitation regimes.

10aAnnual net primary production10aClimate change10aClipping10adisturbance10adiversity10aGrass–forb interaction10aKonza10aPrecipitation10aStem density1 aKoerner, S.E.1 aCollins, Scott., L.1 aBlair, John, M.1 aKnapp, Alan, K.1 aSmith, M.D. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/jvs.1206502035nas a2200145 4500008004100000245007500041210006900116300001500185490000700200520155500207100001701762700002001779700001601799856007401815 2014 eng d00aResistance and resilience of a grassland ecosystem to climate extremes0 aResistance and resilience of a grassland ecosystem to climate ex a2646 -26560 v953 a

Climate change forecasts of more frequent climate extremes suggest that such events will become increasingly important drivers of future ecosystem dynamics and function. Because the rarity and unpredictability of naturally occurring climate extremes limits assessment of their ecological impacts, we experimentally imposed extreme drought and a mid-summer heat wave over two years in a central U.S. grassland. While the ecosystem was resistant to heat waves, it was not resistant to extreme drought, which reduced aboveground net primary productivity (ANPP) below the lowest level measured in this grassland in almost 30 years. This extreme reduction in ecosystem function was a consequence of reduced productivity of both C4 grasses and C3 forbs. However, the dominant forb was negatively impacted by the drought more than the dominant grass, and this led to a reordering of species abundances within the plant community. Although this change in community composition persisted post-drought, ANPP recovered completely the year after drought due to rapid demographic responses by the dominant grass, compensating for loss of the dominant forb. Overall, these results show that an extreme reduction in ecosystem function attributable to climate extremes (e.g., low resistance) does not preclude rapid ecosystem recovery. Given that dominance by a few species is characteristic of most ecosystems, knowledge of the traits of these species and their responses to climate extremes will be key for predicting future ecosystem dynamics and function.

1 aHoover, D.L.1 aKnapp, Alan, K.1 aSmith, M.D. uhttps://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/13-2186.102630nas a2200133 4500008004100000245012400041210006900165300001500234490000700249520212700256100001602383700001602399856008102415 2014 eng d00aResource availability modulates above and belowground competitive interactions between genotypes of a dominant C4 grass0 aResource availability modulates above and belowground competitiv a1041 -10510 v283 a

The well-described pattern of a few common and many rare species in plant communities (dominance-diversity curves) also has been documented within populations of dominant plant species. Understanding how these common genotypes coexist has implications for how genotype richness of a dominant species may impact community and ecosystem processes. Some studies have shown that increased genotype richness of a dominant species leads to an increase in above-ground productivity, suggesting niche complementarity between genotypes. However, mechanistic understanding of how genotypes may complement one another is lacking. We conducted a pairwise competition experiment between four common and naturally co-occurring genotypes of a dominant C4 grass species, Andropogon gerardii, in tallgrass prairie of the central United States. The genotypes were grown under both intra- and intergenotypic competition with different combinations of resources (low and high light, water, and nitrogen) in the greenhouse. We determined that there were above- and below-ground phenotypic differences between genotypes which results in altered competitive interactions depending on resource conditions. Different genotypes were competitively dominant under low- and high-light conditions and low and high N and water availability. Moreover, relative yield total values (RYT) for each genotype pairwise combination indicated that all four genotypes make demands on different resources, providing evidence for niche complementarity. Finally, we found that differential success in resource acquisition, biomass accumulation, and subsequent competitive ability translated to variation in vegetative reproductive success of the genotypes, which has implications for the population dynamics of this primarily asexually reproducing perennial grass. Our results suggest that naturally co-occurring genotypes coexist because they are competitively dominant under different environmental conditions, providing insight into how genetic diversity within dominant plant species is maintained and may potentially affect important ecosystem processes.

1 aChang, C.C.1 aSmith, M.D. uhttps://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2435.1222703618nas a2200385 4500008004100000245009200041210006900133300001300202490000700215520250400222653002202726653001502748653001902763653003702782653002002819653001302839653002202852653001302874653002202887653002702909100001602936700002402952700001602976700002002992700002003012700001603032700001703048700001603065700001803081700001903099700001903118700001703137700001603154856006203170 2014 eng d00aResponses to fire differ between South African and North American grassland communities0 aResponses to fire differ between South African and North America a793 -8040 v253 a

Question Does fire frequency affect mesic grassland plant community structure and composition similarly in North America and South Africa? Location Konza Prairie Biological Station (KNZ), Kansas, USA, and Ukulinga Research Farm (URF), KwaZulu-Natal, South Africa. Methods Plant community structure and composition were compared among annually burned, unburned and intermediate treatments within two long-term fire frequency manipulation experiments in native grasslands in North America and South Africa using comparable methodology over a 5-yr period. Because fire may reduce soil nitrogen (N) availability and thus affect plant community structure, N additions were superimposed on the fire treatments as a means of assessing direct vs indirect mechanisms driving responses to fire. Results The total number of species was higher at URF (183) than at KNZ (57). Overall divergence in plant community response to fire frequency occurred despite similar responses to nutrient additions. At KNZ, more frequent fire resulted in dominance by a few, tall, deep-rooted rhizomatous grasses (e.g. Andropogon gerardii). On unburned sites, shorter, more shade-tolerant species such as Poa pratensis increased in abundance, although A. gerardii remained dominant. Species richness increased with decreasing fire frequency at KNZ. At URF, frequent fire resulted in short, diverse grassland weakly dominated by a range of grass species, including Themeda triandra, Tristachya leucothrix and Hyparrhenia hirta. Decreasing fire frequency reduced species richness and resulted in dominance by a few, relatively tall caespitose grasses such as Aristida junciformis. There was a complete turnover of dominant species between annually burned and unburned treatments at URF, while at KNZ A. gerardii and Sorghastrum nutans occurred across the range of treatments. N addition reduced species richness in both sites. Conclusions Different responses to fire frequency between KNZ and URF are likely linked to the dominant species and their characteristic traits, including height and method of clonal reproduction, with the rhizomatous growth form of A. gerardii dominating the North American grassland. South Africa does not have an equivalent grass species; instead, a range of tufted, non-rhizomatous species dominate across the fire frequency treatments at URF. Reductions in soil N due to frequent fire did not appear to be a common mechanism driving responses in community composition in these two grasslands.

10aCommunity ecology10aDivergence10aFire frequency10aKonza Prairie Biological Station10aMesic grassland10anitrogen10aNutrient addition10aRichness10atallgrass prairie10aUkulinga Research Farm1 aKirkman, K.1 aCollins, Scott., L.1 aSmith, M.D.1 aKnapp, Alan, K.1 aBurkepile, D.E.1 aBurns, C.E.1 aFynn, R.W.S.1 aHagenah, N.1 aKoerner, S.E.1 aMatchett, K.J.1 aThompson, D.I.1 aWilcox, K.R.1 aWragg, P.D. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/jvs.1213001778nas a2200325 4500008004100000245012500041210006900166300001300235490000700248520081800255100001701073700001601090700001801106700001601124700002201140700001701162700001701179700001801196700002401214700001601238700002001254700001301274700001301287700001201300700001601312700001601328700001801344700001901362856007101381 2013 eng d00aCoordinated distributed experiments: an emerging tool for testing global hypotheses in ecology and environmental science0 aCoordinated distributed experiments an emerging tool for testing a147 -1550 v113 a

There is a growing realization among scientists and policy makers that an increased understanding of today's environmental issues requires international collaboration and data synthesis. Meta-analyses have served this role in ecology for more than a decade, but the different experimental methodologies researchers use can limit the strength of the meta-analytic approach. Considering the global nature of many environmental issues, a new collaborative approach, which we call coordinated distributed experiments (CDEs), is needed that will control for both spatial and temporal scale, and that encompasses large geographic ranges. Ecological CDEs, involving standardized, controlled protocols, have the potential to advance our understanding of general principles in ecology and environmental science.

1 aFraser, L.H.1 aHenry, H.A.1 aCarlyle, C.N.1 aWhite, S.R.1 aBeierkuhnlein, C.1 aCahill, J.F.1 aCasper, B.B.1 aCleland, E.E.1 aCollins, Scott., L.1 aDukes, J.S.1 aKnapp, Alan, K.1 aLind, E.1 aLong, R.1 aLuo, Y.1 aReich, P.B.1 aSmith, M.D.1 aSternberg, M.1 aTurkington, R. uhttps://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/11027903057nas a2200217 4500008004100000245010300041210006900144300001500213490000700228520234600235653002402581653001302605653002102618653001402639653002702653653002202680653004202702100001702744700001602761856006202777 2013 eng d00aCorrelations between genetic and species diversity: effects of resource quantity and heterogeneity0 aCorrelations between genetic and species diversity effects of re a1185 -11940 v243 a

Questions It is hypothesized that species and genetic diversity are correlated because niche differentiation among species and genotypes is either affected by the same processes (positive) or each level restricts the amount of diversity in the other (negative). Although many studies have observed both positive and negative relationships, others have found no correlation between the two diversity measures. Are measures of species (richness, diversity and evenness) and genetic diversity correlated, and how does resource (soil moisture, light, nitrogen and phosphorus) quantities and heterogeneity affect both levels of diversity? Location Intact tallgrass prairie at Konza Prairie Biological Station, northeast Kansas, US. Methods We investigate the correlation between plant species and genetic diversity in a long-term precipitation manipulation experiment – the Rainfall Manipulation Plots (RaMPs) – located in intact tallgrass prairie as well as adjacent non-manipulated prairie. The RaMPs experiment has been imposing ambient and more variable precipitation regimes (a 50% increase in timing between rainfall events without changing total rainfall amount) during the growing season since 1998, resulting in reduced mean soil moisture and increased soil moisture variability. Thus, the RaMPs and non-manipulated prairie plots capture a range of soil moisture amounts and variability. Genetic diversity (measured as genotype richness and genomic dissimilarity among individuals) was quantified for the dominant grass species, Andropogon gerardii, which has large impacts on plant community structure and ecosystem function. Results We found species and genetic diversity were not significantly correlated. Genotypic richness was negatively related to soil moisture variability, but measures of species diversity were not. In the non-manipulated plots only, we found generally negative relationships between resource quantity (light and nitrogen) and community diversity, and positive relationships between resource heterogeneity (CV of light) and community diversity. Conclusions Our results suggest that a lack of a positive or negative relationship between species and genetic diversity could be due to these two levels of diversity responding differently to the identity, quantity and heterogeneity of resources.

10aAndropogon gerardii10aC4 grass10adominant species10agrassland10aResource heterogeneity10aResource quantity10aSpecies genetic diversity correlation1 aAvolio, M.L.1 aSmith, M.D. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/jvs.1204200577nas a2200121 4500008004100000245017400041210006900215260003500284490002100319100002800340700001600368856007100384 2013 eng d00aDrivers of grassland community structure and ecosystem function: the role of biotic factors in determining the ecosystem response to alterations in resource availability0 aDrivers of grassland community structure and ecosystem function  aNew Haven, CTbYale University0 vPhD Dissertation1 aLa Pierre, Kimberly, J.1 aSmith, M.D. uhttp://search.proquest.com/docview/1495948277?pq-origsite=gscholar02499nas a2200205 4500008004100000245009700041210006900138300001300207490000800220520184800228653000902076653002402085653002302109653002102132653002402153100001702177700001702194700001602211856006602227 2013 eng d00aGenetic diversity of a dominant C4 grass is altered with increased precipitation variability0 aGenetic diversity of a dominant C4 grass is altered with increas a571 -5810 v1713 a

Climate change has the potential to alter the genetic diversity of plant populations with consequences for community dynamics and ecosystem processes. Recent research focused on changes in climatic means has found evidence of decreased precipitation amounts reducing genetic diversity. However, increased variability in climatic regimes is also predicted with climate change, but the effects of this aspect of climate change on genetic diversity have yet to be investigated. After 10 years of experimentally increased intra-annual variability in growing season precipitation regimes, we report that the number of genotypes of the dominant C4 grass, Andropogon gerardii Vitman, has been significantly reduced in native tallgrass prairie compared with unmanipulated prairie. However, individuals showed a different pattern of genomic similarity with increased precipitation variability resulting in greater genome dissimilarity among individuals when compared to unmanipulated prairie. Further, we found that genomic dissimilarity was positively correlated with aboveground productivity in this system. The increased genomic dissimilarity among individuals in the altered treatment alongside evidence for a positive correlation of genomic dissimilarity with phenotypic variation suggests ecological sorting of genotypes may be occurring via niche differentiation. Overall, we found effects of more variable precipitation regimes on population-level genetic diversity were complex, emphasizing the need to look beyond genotype numbers for understanding the impacts of climate change on genetic diversity. Recognition that future climate change may alter aspects of genetic diversity in different ways suggests possible mechanisms by which plant populations may be able to retain a diversity of traits in the face of declining biodiversity.

10aAFLP10aAndropogon gerardii10aDice dissimilarity10adominant species10aGenotypic structure1 aAvolio, M.L.1 aBeaulieu, J.1 aSmith, M.D. uhttps://link.springer.com/article/10.1007%2Fs00442-012-2427-402994nas a2200229 4500008004100000245009000041210006900131300001300200490000600213520223900219653002402458653002602482653002402508653004302532653002202575653004002597653001702637653002202654100001602676700001602692856005602708 2013 eng d00aGenotypic diversity of a dominant C4 grass across a long-term fire frequency gradient0 aGenotypic diversity of a dominant C4 grass across a longterm fir a448 -4580 v63 a

Aims and Methods Diversity-disturbance research has focused on community diversity, but disturbance frequency could impact diversity within species as well, with important consequences for community diversity and ecosystem function. We examined patterns of genetic diversity of a dominant grass species, Andropogon gerardii, in native North American tallgrass prairie sites located in eastern Kansas that have been subjected to a gradient of fire frequency treatments (burned every 1, 2, 4 or 20 years) since the 1970s. In addition, we were able to assess the relationships between genetic diversity of A. gerardii, species diversity and productivity across this range of fire frequencies. Important Findings We found no significant relationships between genetic diversity of A. gerardii at the local scale (1 m2 plot level) and disturbance frequency (burned 2 to 32 times over a 38-year period). However, at the site level (i.e. across all plots sampled within a site, ~100 m2) there were differences in genotype richness and composition, as well as genomic dissimilarity among individuals of A. gerardii. Genotype richness was greatest for the site burned at an intermediate (4-year) frequency and lowest for the infrequently (20-year) burned site. In addition, genotypes found in the frequently burned sites were more similar from each other than expected by random chance than those found in the infrequently burned sites. Genotype composition of A. gerardii was not significantly different between the frequently burned sites (annual vs. 2 year) but did differ between frequently burned and infrequently burned sites (1 and 2 year vs. 4 and 20 year, etc.). Together, these results suggest site-level ecological sorting of genotypes in intact prairie across a broad gradient of disturbance frequencies, likely driven by alterations in environmental conditions. Frequent fire promotes the abundance of dominant grass species, reduces plant community diversity and impacts ecosystem processes such as productivity. Our study suggests that genetic diversity within dominant grass species also may be affected by disturbance frequency, which could have important implications for how species are able to respond to disturbance.

10aAndropogon gerardii10adisturbance frequency10agenetic relatedness10agenetic-species diversity relationship10agenotype richness10aintermediate disturbance hypothesis10aproductivity10atallgrass prairie1 aChang, C.C.1 aSmith, M.D. uhttps://academic.oup.com/jpe/article/6/6/448/98097702136nas a2200133 4500008004100000245008600041210006900127300001600196490000800212520169400220100001701914700001601931856005501947 2013 eng d00aIntra-specific responses of a dominant C4 grass to altered precipitation patterns0 aIntraspecific responses of a dominant C4 grass to altered precip a1377 - 13890 v2143 a

The mechanisms by which global change alters the genotypic structure of populations by selection remain unclear. Key to this understanding is elucidating genotype–phenotype relationships under different environmental conditions as genotypes could differ in their plasticity or in their tolerance to changing environmental conditions. We have previously observed selection of certain genotypes of the dominant C4 grass Andropogon gerardii L. within the on-going Rainfall Manipulation Plots (RaMPs) experiment at Konza Prairie Biological Station in Kansas. The RaMPs experiment has been experimentally imposing ambient and more variable (altered) precipitation patterns since 1998. Here, we studied phenotypic differences among six genotypes to gain insight into what drove the pattern of selection previously observed and assess potential genotype × environmental interactions. In 2008 and 2009 we sampled individuals of genotypes in the RaMPs and within unmanipulated reference plots located adjacent to the RaMPs experiment. For each individual, we measured both leaf-level (specific leaf area, stomatal conductance) and whole-plant growth (height, biomass) traits. We consistently detected differences among genotypes in the reference plots. Additionally, when focusing on two genotypes found in the altered and ambient RaMPs we observed no genotype × environment interactions. Overall, we found in an intact population of A. gerardii there exists phenotypic variability among genotypes, but no genotype × environment interactions. Thus our results demonstrate that differences in plasticity of genotypes do no explain the pattern of selection we observed.

1 aAvolio, M.L.1 aSmith, M.D. uhttp://link.springer.com/10.1007/s11258-013-0258-y02711nas a2200133 4500008004100000245012000041210006900161300001300230490000700243520222000250100001702470700001602487856007402503 2013 eng d00aMechanisms of selection: Phenotypic differences among genotypes explain patterns of selection in a dominant species0 aMechanisms of selection Phenotypic differences among genotypes e a953 -9650 v943 a

Predicted changes in precipitation means and variability are expected to alter genotype composition of plant populations; however, it remains unclear whether selection will be for trait differences among genotypes or phenotypic plasticity. This is especially true for more variable precipitation patterns that simultaneously alter soil moisture means and variability. In a previous study we found that a decade of more variable growing-season precipitation patterns changed the genotypic composition of a dominant C4 grass population (Andropogon gerardii) in native tallgrass prairie located in northeastern Kansas. Here, we assessed potential mechanisms underlying the changes observed in population structure of this species by studying how changes in both the size and variability of watering events affected ecophysiological, growth, biomass-allocation, and fitness traits of five common genotypes of A. gerardii in a greenhouse experiment. Three of these genotypes had greater abundances or were only present in field plots receiving 10 years of greater intra-annual variability in growing-season precipitation patterns. In a fully factorial experiment, we subjected the five genotypes to three water amounts (average for Kansan study site, a 40% decrease, and a 60% increase) and two watering frequency treatments (every 5 or 10 days) to produce differences in soil moisture amount and variability, respectively. We found genotype × water amount interactions for traits related to leaf-level physiology and biomass allocation; in many cases genotypes that performed better under low soil moisture conditions were outperformed by other genotypes under high soil moisture conditions. For the three genotypes that had greater abundance in field plots that received more variable precipitation patterns, we found evidence that genotypes differed in their allocation to above- vs. belowground biomass, demonstrating phenotypic trait divergence. Our results suggest that a genetically diverse population can have enough trait variation among genotypes for adaptation to occur, and thus, for dominant species, microevolution may be an important aspect of adaptation to changing environmental conditions.

1 aAvolio, M.L.1 aSmith, M.D. uhttps://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/12-1119.104613nas a2200985 4500008004100000245010500041210006900146300001600215490000700231520209700238100001902335700001602354700001602370700001802386700001502404700001302419700001802432700001602450700001302466700001902479700001702498700001702515700001402532700001602546700001902562700001702581700002002598700002102618700001602639700001802655700001702673700001202690700001802702700001402720700001902734700002002753700002002773700001802793700001102811700001402822700001502836700001702851700001602868700001502884700001302899700001902912700002002931700002002951700001702971700001402988700001203002700001803014700001603032700001803048700002803066700001503094700002003109700001903129700001103148700001103159700001703170700001803187700001903205700002203224700001703246700001803263700002103281700001603302700001503318700001503333700001403348700002303362700001703385700001603402700001703418700001603435700001603451700001703467700001703484700002003501700001603521700001503537700001303552856006203565 2013 eng d00aPredicting invasion in grassland ecosystems: is exotic dominance the real embarrassment of richness?0 aPredicting invasion in grassland ecosystems is exotic dominance  a3677 - 36870 v193 a

Invasions have increased the size of regional species pools, but are typically assumed to reduce native diversity. However, global-scale tests of this assumption have been elusive because of the focus on exotic species richness, rather than relative abundance. This is problematic because low invader richness can indicate invasion resistance by the native community or, alternatively, dominance by a single exotic species. Here, we used a globally replicated study to quantify relationships between exotic richness and abundance in grass-dominated ecosystems in 13 countries on six continents, ranging from salt marshes to alpine tundra. We tested effects of human land use, native community diversity, herbivore pressure, and nutrient limitation on exotic plant dominance. Despite its widespread use, exotic richness was a poor proxy for exotic dominance at low exotic richness, because sites that contained few exotic species ranged from relatively pristine (low exotic richness and cover) to almost completely exotic-dominated ones (low exotic richness but high exotic cover). Both exotic cover and richness were predicted by native plant diversity (native grass richness) and land use (distance to cultivation). Although climate was important for predicting both exotic cover and richness, climatic factors predicting cover (precipitation variability) differed from those predicting richness (maximum temperature and mean temperature in the wettest quarter). Herbivory and nutrient limitation did not predict exotic richness or cover. Exotic dominance was greatest in areas with low native grass richness at the site- or regional-scale. Although this could reflect native grass displacement, a lack of biotic resistance is a more likely explanation, given that grasses comprise the most aggressive invaders. These findings underscore the need to move beyond richness as a surrogate for the extent of invasion, because this metric confounds monodominance with invasion resistance. Monitoring species' relative abundance will more rapidly advance our understanding of invasions.

1 aSeabloom, E.W.1 aBorer, E.T.1 aBuckley, Y.1 aCleland, E.E.1 aDavies, K.1 aFirn, J.1 aHarpole, W.S.1 aHautier, Y.1 aLind, E.1 aMacDougall, A.1 aOrrock, J.L.1 aProber, S.M.1 aAdler, P.1 aAlberti, J.1 aAnderson, M.T.1 aBakker, J.D.1 aBiederman, L.A.1 aBlumenthal, D.M.1 aBrown, C.S.1 aBrudvig, L.A.1 aCaldeira, M.1 aChu, C.1 aCrawley, M.J.1 aDaleo, P.1 aDamschen, E.I.1 aD'Antonio, C.M.1 aDeCrappeo, N.M.1 aDickman, C.R.1 aDu, G.1 aFay, P.A.1 aFrater, P.1 aGruner, D.S.1 aHagenah, N.1 aHector, A.1 aHelm, A.1 aHillebrand, H.1 aHofmockel, K.S.1 aHumphries, H.C.1 aIribarne, O.1 aJin, V.L.1 aKay, A.1 aKirkman, K.P.1 aKlein, J.A.1 aKnops, J.M.H.1 aLa Pierre, Kimberly, J.1 aLadwig, L.1 aLambrinos, J.G.1 aLeakey, A.D.B.1 aLi, Q.1 aLi, W.1 aMcCulley, R.1 aMelbourne, B.1 aMitchell, C.E.1 aMoore, Joslin, L.1 aMorgan, J.W.1 aMortensen, B.1 aO'Halloran, L.R.1 aPärtel, M.1 aPascual, J1 aPyke, D.A.1 aRisch, A.1 aSalguero-Gomez, R.1 aSankaran, M.1 aSchuetz, M.1 aSimonsen, A.1 aSmith, M.D.1 aStevens, C.1 aSullivan, L.1 aWardle, G.M.1 aWolkovich, E.M.1 aWragg, P.D.1 aWright, J.1 aYang, L. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.1237000506nas a2200133 4500008004100000245009500041210006900136300001500205490000700220100002000227700001900247700001600266856009000282 2012 eng d00aCommunity stability does not preclude ecosystem sensitivity to chronic resource alteration0 aCommunity stability does not preclude ecosystem sensitivity to c a1231 -12330 v261 aKnapp, Alan, K.1 aBriggs, J., M.1 aSmith, M.D. uhttps://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2435.2012.02053.x04283nas a2200145 4500008004100000245010900041210006900150260003500219300001100254490002100265520376900286100001604055700001604071856005004087 2012 eng d00aDimensions of diversity and their direct and indirect effects on tallgrass prairie ecosystem functioning0 aDimensions of diversity and their direct and indirect effects on aNew Haven, CTbYale University a1 -1650 vPhD Dissertation3 a

Understanding the role of biological diversity to ecosystem function in ecological communities is particularly important now in the face of unprecedented, human-driven global change. Anthropogenic impacts such as climate change, nitrogen deposition, and land-use changes that modify natural disturbance regimes and promote the introduction of invasive species are all altering environmental conditions in such a way as to impact both diversity and ecosystem functioning. Diversity can be described in several ways and until recently, most research has focused on the relationship between the number and diversity of species and ecosystem function. Recently however, there has been a growing focus on the importance of genetic diversity within a dominant species and its impact on community and ecosystem processes. In this dissertation, I examine the relationship between community and population diversity, evaluate how diversity at both levels is maintained under varying environmental conditions, and test the relative effects of population and community level diversity on ecosystem function. First, I utilized a long-term experimental burn manipulation to examine the impact of fire frequency on genetic diversity of the dominant species and assessed the relationship between genetic diversity of the dominant species, species diversity, and productivity across the entire fire gradient. Genetic diversity of the dominant species was highest in a four year burn cycle and lowest in an annual and two year burn cycle. However, there was not a significant relationship between genetic and species diversity or between genetic diversity of the dominant species and productivity across the disturbance Gradient. In the second and third study, I explored in further detail the relationship between genetic diversity of the dominant species, species diversity, and evaluate the direct and indirect effects of both levels of diversity on productivity and invasion resistance. Contrary to expectations, genetic diversity of the dominant species did not have a direct effect on invasion resistance or productivity. Rather the effects of diversity at both the community and population level are primarily indirect via traits. Genetic differences between naturally co-occurring genotypes of the perennial dominant grass species were more subtle, and thus also highlighted the necessity of conducting studies in intact communities with naturally co-occurring individuals. Finally, to tease apart the possible mechanisms for how diversity within the population is maintained and subsequently impacts community and ecosystem processes, I conducted a pairwise competition experiment with the four most common genotypes of the dominant species and manipulated light, water, and nitrogen resources. Phenotypic differences between genotypes resulted in different competitive successes depending on resource conditions. Some genotypes were able to take advantage of increased water or nitrogen resources under low and high light conditions, providing evidence for niche complementarity. There was evidence that some genotypes were more antagonistic under low versus high resource conditions while other genotypes were more synergistic. This differential success in resource acquisition, biomass accumulation, and subsequent competitive ability translated to variation in vegetative reproductive success, which has implications for the population dynamics of this perennial, primarily asexually reproductive, dominant C4 grass. Together the results from these four studies suggest that the roles of population and community level diversity are complex in intact, natural tallgrass prairie where diversity effects on ecosystem function may be primarily indirect via traits.

1 aChang, C.C.1 aSmith, M.D. uhttp://search.proquest.com/docview/103955454705437nas a2200145 4500008004100000245011000041210006900151260003500220300001100255490002100266520492100287100001705208700001605225856005005241 2012 eng d00aGenetic diversity of Andropogon gerardii: Impacts of altered precipitation patterns on a dominant species0 aGenetic diversity of Andropogon gerardii Impacts of altered prec aNew Haven, CTbYale University a1 -2580 vPhD Dissertation3 a

Global change is expected to shift climatic regimes and cause whole communities of organisms to experience novel environments. Key aspects of forecast climate change are alterations in both the amount of precipitation and the variability of precipitation regimes. The ability of a population to adapt will depend on the genetic diversity of the population, and the traits of the genotypes present in the population. Here, I assess the response a dominant C4 tallgrass population to novel environmental conditions resulting from forecast climate change by studying whether more variable precipitation patterns affect the genetic diversity of Andropogon gerardii. I then investigate the potential mechanisms driving the observed response. Ultimately, the way in which population genetic diversity is affected by more variable precipitation patterns will shed insight into how this important species will adapt to future climate change. First, I developed the tools to study the genetic diversity of A. gerardii at the plant neighborhood scale, the scale at which individuals compete for resources. I designed amplified fragment length polymorphism primers for A. gerardii and determined the appropriate scale at which to sample individuals to accurately capture genetic diversity. I also examined how genetic diversity is measured in ecological studies by comparing genotype-based measures and genome-based measures of diversity. Ultimately, I argue that genome-based measures should be included in future studies alongside genotypic-based measures because they capture a greater spectrum of genetic differences among individuals. Next, using what I established for studying genetic diversity, I examined how a decade of altered precipitation patterns affected the genetic diversity of A. gerardii. To do this I worked within the Rainfall Manipulation Plots (RaMPs) experiment at Konza Prairie Biological Station in Kansas, which experimentally imposes ambient and more variable precipitation patterns. After ten years of experimentally increased intra-annual variability in growing season precipitation regimes, I report that the number of genotypes of the dominant C4 grass, Andropogon gerardii Vitman, has been significantly reduced in native tallgrass prairie compared with unmanipulated prairie. However, individuals showed a different pattern of genomic similarity with increased precipitation variability – there was greater genome dissimilarity among individuals when compared to unmanipulated prairie. In my next two chapters, I aim to understand the mechanism that drove the observed shift in genetic diversity. First, I studied phenotypic differences among six common genotypes of Andropogon gerardii across three different environmental conditions to study genotype × environmental interactions. I consistently detected differences among the focal genotypes for all traits measured across environmental treatments, however, I observed no genotype × year interactions, and phenotypic differences among genotypes were diminished within environmental conditions. To assess potential mechanisms underlying the changes observed in population structure of this species, I continued to study five of the same genotypes, three of which had greater abundances or were only present in plots receiving more variable rainfall patterns. In a greenhouse study, I investigated how both changes in the size and variability of watering events affected ecophysiological, growth, biomass allocation and fitness traits. I found genotype × water amount interactions for traits related to leaf level physiology and biomass allocation; genotypes that performed better under low soil moisture conditions were outperformed by other genotypes under high soil moisture conditions. For the three genotypes that had greater abundance in plots that received a decade of altered rainfall regimes, I found evidence of phenotypic trait divergence as well as greater plasticity for ecophysiological traits. Lastly, I investigated correlations between species and genetic diversity in tallgrass prairie across an experimental manipulation of soil moisture. I found species and genetic diversity were not correlated, and that genotypic richness was negatively related to soil moisture variability, but measures of species diversity were not related to soil moisture. My results suggest that a lack relationship between species and genetic diversity at the populations scale could be because species and genetic diversity are responding differently to environmental resources. Ultimately, my dissertation is an in-depth examination of how environmental conditions affect the genetic diversity of a dominant species. I found that for genetically diverse species, such as dominant species, microevolution might be an important aspect of adaptation to novel environmental conditions experienced with climate change.

1 aAvolio, M.L.1 aSmith, M.D. uhttp://search.proquest.com/docview/127202895602383nas a2200193 4500008004100000245009600041210006900137300001500206490000800221520176000229653002301989653002102012653002202033653001402055653002202069100001602091700001602107856006602123 2012 eng d00aInvasion of an intact plant community: the role of population vs. community level diversity0 aInvasion of an intact plant community the role of population vs  a1091 -11020 v1683 a

To improve the understanding of how native plant diversity influences invasion, we examined how population and community diversity may directly and indirectly be related to invasion in a natural field setting. Due to the large impact of the dominant C4 grass species (Andropogon gerardii) on invasion resistance of tallgrass prairie, we hypothesized that genetic diversity and associated traits within a population of this species would be more strongly related to invasion than diversity or traits of the rest of the community. We added seeds of the exotic invasive C4 grass, A. bladhii, to 1-m2 plots in intact tallgrass prairie that varied in genetic diversity of A. gerardii and plant community diversity, but not species richness. We assessed relationships among genetic diversity and traits of A. gerardii, community diversity, community aggregated traits, resource availability, and early season establishment and late-season persistence of the invader using structural equation modeling (SEM). SEM models suggested that community diversity likely enhanced invasion indirectly through increasing community aggregated specific leaf area as a consequence of more favorable microclimatic conditions for seedling establishment. In contrast, neither population nor community diversity was directly or indirectly related to late season survival of invasive seedlings. Our research suggests that while much of diversity–invasion research has separately focused on the direct effects of genetic and species diversity, when taken together, we find that the role of both levels of diversity on invasion resistance may be more complex, whereby effects of diversity may be primarily indirect via traits and vary depending on the stage of invasion.

10aAndropogon bladhii10adominant species10agenetic diversity10agrassland10atallgrass prairie1 aChang, C.C.1 aSmith, M.D. uhttps://link.springer.com/article/10.1007%2Fs00442-011-2157-z02191nas a2200217 4500008004100000245005400041210005400095300001500149490000800164520158300172653002401755653002301779653002101802653001401823653000901837100001701846700001701863700001101880700001601891856006601907 2012 eng d00aMeasuring genetic diversity in ecological studies0 aMeasuring genetic diversity in ecological studies a1105 -11150 v2133 a

There is an increasing interest in how genetic diversity may correlate with and influence community and ecosystem properties. Genetic diversity can be defined in multiple ways, and currently lacking in ecology is a consensus on how to measure genetic diversity. Here, we examine two broad classes of genetic diversity: genotype-based and genome-based measures. Genotype-based measures, such as genotypic richness, are more commonly used in ecological studies, and often it is assumed that as genotypic diversity increases, genomic diversity (the number of genetic polymorphisms and/or genomic dissimilarity among individuals) also increases. However, this assumption is rarely assessed. We tested this assumption by investigating correlations between genotype- and genome-based measures of diversity using two plant population genetic datasets: one observational with data collected at Konza Prairie, KS, and the other based on simulated populations with five levels of genotypic richness, a typical design of genetic diversity experiments. We found conflicting results for both datasets; we found a mismatch between genotypic and genomic diversity measures for the field data, but not the simulated data. Last, we tested the consequences of this mismatch and found that correlations between genetic diversity and community/ecosystem properties depended on metric used. Ultimately, we argue that genome-based measures should be included in future studies alongside genotypic-based measures because they capture a greater spectrum of genetic differences among individuals.

10aCommunity diversity10aEcosystem function10aGenome diversity10aPhenotype10aSGDC1 aAvolio, M.L.1 aBeaulieu, J.1 aLo, E.1 aSmith, M.D. uhttps://link.springer.com/article/10.1007%2Fs11258-012-0069-602050nas a2200313 4500008004100000245008100041210006900122300001300191490000700204520112700211653001901338653001801357653002301375653001701398653002801415100002001443700001601463700001701479700002401496700001601520700001901536700001701555700002801572700001801600700001901618700001701637700001801654856006401672 2012 eng d00aPast, present, and future roles of long-term experiments in the LTER Network0 aPast present and future roles of longterm experiments in the LTE a377 -3890 v623 a

The US National Science Foundation–funded Long Term Ecological Research (LTER) Network supports a large (around 240) and diverse portfolio of long-term ecological experiments. Collectively, these long-term experiments have (a) provided unique insights into ecological patterns and processes, although such insight often became apparent only after many years of study; (b) influenced management and policy decisions; and (c) evolved into research platforms supporting studies and involving investigators who were not part of the original design. Furthermore, this suite of long-term experiments addresses, at the site level, all of the US National Research Council's Grand Challenges in Environmental Sciences. Despite these contributions, we argue that the scale and scope of global environmental change requires a more-coordinated multisite approach to long-term experiments. Ideally, such an approach would include a network of spatially extensive multifactor experiments, designed in collaboration with ecological modelers that would build on and extend the unique context provided by the LTER Network.

10aClimate change10aglobal change10along-term research10aLTER Network10amultifactor experiments1 aKnapp, Alan, K.1 aSmith, M.D.1 aHobbie, S.E.1 aCollins, Scott., L.1 aFahey, T.J.1 aHansen, G.J.A.1 aLandis, D.A.1 aLa Pierre, Kimberly, J.1 aMelillo, J.M.1 aSeastedt, T.R.1 aShaver, G.R.1 aWebster, J.R. uhttps://academic.oup.com/bioscience/article/62/4/377/24376203337nas a2200349 4500008004100000245011600041210006900157300001300226490000600239520233700245653003902582653000902621653001002630653001502640653001202655100002002667700001702687700002002704700001302724700002002737700002202757700002402779700001702803700001802820700001602838700001402854700001702868700001702885700001602902700001302918856005602931 2012 eng d00aA test of two mechanisms proposed to optimize grassland aboveground primary productivity in response to grazing0 atest of two mechanisms proposed to optimize grassland abovegroun a357 -3650 v53 a

Aims Mesic grasslands have a long evolutionary history of grazing by large herbivores and as a consequence, grassland species have numerous adaptations allowing them to respond favourably to grazing. Although empirical evidence has been equivocal, theory predicts that such adaptations combined with alterations in resources can lead to grazing-induced overcompensation in aboveground net primary production (ANPP; grazed ANPP > ungrazed ANPP) under certain conditions. We tested two specific predictions from theory. First, overcompensation is more likely to occur in annually burned grasslands because limiting nutrients that would be lost with frequent fires are recycled through grazers and stimulate ANPP. Second, overcompensation of biomass lost to grazers is more likely to occur in unburned sites where grazing has the greatest effect on increasing light availability through alterations in canopy structure. Methods We tested these nutrient versus light-based predictions in grazed grasslands that had been annually burned or protected from fire for >20 years. We assessed responses in ANPP to grazing by large ungulates using both permanent and moveable grazing exclosures (252 exclosures from which biomass was harvested from 3192 quadrats) in a 2-year study. Study sites were located at the Konza Prairie Biological Station (KPBS) in North America and at Kruger National Park (KNP) in South Africa. At KPBS, sites were grazed by North American bison whereas in KNP sites were grazed either by a diverse suite of herbivores (e.g. blue wildebeest, Burchell’s zebra, African buffalo) or by a single large ungulate (African buffalo). Important Findings We found no evidence for overcompensation in either burned or unburned sites, regardless of grazer type. Thus, there was no support for either mechanism leading to overcompensation. Instead, complete compensation of total biomass lost to grazers was the most common response characterizing grazing–ANPP relationships with, in some cases, undercompensation of grass ANPP being offset by increased ANPP of forbs likely due to competitive release. The capability of these very different grass-dominated systems to maintain ANPP while being grazed has important implications for energy flow, ecosystem function and the trophic dynamics of grasslands.

10aaboveground net primary production10afire10aforbs10aherbivores10asavanna1 aKnapp, Alan, K.1 aHoover, D.L.1 aBlair, John, M.1 aBuis, G.1 aBurkepile, D.E.1 aChamberlain, A.J.1 aCollins, Scott., L.1 aFynn, R.W.S.1 aKirkman, K.P.1 aSmith, M.D.1 aBlake, D.1 aGovender, N.1 aO’Neal, P.1 aSchreck, T.1 aZinn, A. uhttps://academic.oup.com/jpe/article/5/4/357/90869501387nas a2200145 4500008004100000245008800041210006900129300001300198490000800211520092500219100001701144700001601161700001601177856004801193 2011 eng d00aAssessing fine-scale genotypic structure of a dominant species in native grasslands0 aAssessing finescale genotypic structure of a dominant species in a211 -2240 v1653 a

Genotypic diversity of dominant species has been shown to have important consequences for community and ecosystem processes at a fine spatial scale. We examined the fine-scale (i.e., plant neighborhood scale, <1 m2) genotypic structure of Andropogon gerardii, a dominant species in the tallgrass prairie, which is a productive and endangered grassland ecosystem, employing the commonly used amplified fragment length polymorphism (AFLP) technique. In this paper we used two methods to assess the fine-scale genetic spatial structure of a dominant perennial grass, (1) we determined how many tillers to sample in a 1 m2 area and (2) we developed AFLP markers that would differentiate between genotypes. By determining appropriate sampling and molecular techniques, our findings can be applied to questions addressing how genetic diversity of dominant species affect ecosystem processes in the tallgrass prairie.

1 aAvolio, M.L.1 aChang, C.C.1 aSmith, M.D. uhttps://doi.org/10.1674/0003-0031-165.2.21102725nas a2200193 4500008004100000245011900041210006900160300001500229490000700244520206400251100002802315700001502343700001602358700001702374700001802391700001602409700001602425856009002441 2011 eng d00aExplaining temporal variation in above-ground productivity in a mesic grassland: the role of climate and flowering0 aExplaining temporal variation in aboveground productivity in a m a1250 -12620 v993 a

1. Annual above-ground net primary productivity (ANPP) in mesic grasslands is known to be highly temporally variable. While yearly precipitation or average yearly temperature can explain some of this temporal variability, much of the variation in ANPP remains unexplained. 2. Here we address the heretofore unexplained variation in 25 years of productivity data from a mesic grassland at Konza Prairie (north-eastern Kansas) by examining the effects of precipitation and temperature during periods relevant to the phenology and growth cycle of the dominant C4 grasses and the flowering stalk production of these species. We assessed both the direct effects and indirect effects via flowering of phenologically relevant climate periods on ANPP using structural equation modelling (SEM). 3. We found ANPP to be strongly positively influenced by flowering stalk production of the dominant C4 grasses, precipitation during periods relevant to vegetative growth (15 April–14 July) and flowering stalk elongation (15 July–14 August) of the dominant grasses, and fire. In addition, flowering stalk production was negatively influenced by high temperatures during the flowering stalk elongation period, which therefore resulted in a negative indirect effect on ANPP. We found little evidence for the effects of the previous year’s total annual precipitation or mean annual temperature on ANPP. 4. By including flowering stalk production and separating climate variables into phenologically relevant periods we were able to increase the percentage of observed variance in ANPP explained by six models, relating to different topographic positions and burn regimes, from an average of 22% to 48%, with the best model explaining 61% of variation in ANPP. 5.Synthesis. The link between climatic periods relevant to the phenology and growth of dominant C4 grasses, flowering stalk production of these grasses and ANPP shown here improves our ability to predict productivity in mesic grasslands, an ecologically and economically important ecosystem.

1 aLa Pierre, Kimberly, J.1 aYuan, S.H.1 aChang, C.C.1 aAvolio, M.L.1 aHallett, L.M.1 aSchreck, T.1 aSmith, M.D. uhttps://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2745.2011.01844.x02083nas a2200337 4500008004100000245008000041210006900121300001300190490000600203520111900209100002401328700002001352700001801372700002001390700001901410700001801429700001601447700001601463700001701479700001501496700002001511700001801531700001901549700001901568700001701587700001601604700002001620700001601640700001801656856007101674 2011 eng d00aAn integrated conceptual framework for long-term social-ecological research0 aintegrated conceptual framework for longterm socialecological re a351 -3570 v93 a

The global reach of human activities affects all natural ecosystems, so that the environment is best viewed as a social–ecological system. Consequently, a more integrative approach to environmental science, one that bridges the biophysical and social domains, is sorely needed. Although models and frameworks for social–ecological systems exist, few are explicitly designed to guide a long-term interdisciplinary research program. Here, we present an iterative framework, “Press–Pulse Dynamics” (PPD), that integrates the biophysical and social sciences through an understanding of how human behaviors affect “press” and “pulse” dynamics and ecosystem processes. Such dynamics and processes, in turn, influence ecosystem services –thereby altering human behaviors and initiating feedbacks that impact the original dynamics and processes. We believe that research guided by the PPD framework will lead to a more thorough understanding of social–ecological systems and generate the knowledge needed to address pervasive environmental problems.

1 aCollins, Scott., L.1 aCarpenter, S.R.1 aSwinton, S.M.1 aOrenstein, D.E.1 aChilders, D.L.1 aGragson, T.L.1 aGrimm, N.B.1 aGrove, J.M.1 aHarlan, S.L.1 aKaye, J.P.1 aKnapp, Alan, K.1 aKofinas, G.P.1 aMagnuson, J.J.1 aMcDowell, W.H.1 aMelack, J.M.1 aOgden, L.A.1 aRobertson, G.R.1 aSmith, M.D.1 aWhitmer, A.C. uhttps://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/10006802899nas a2200181 4500008004100000245010200041210006900143300001500212490000600227520232400233100001402557700002002571700001602591700002302607700001902630700002002649856004802669 2011 eng d00aRelative effects of precipitation variability and warming on tallgrass prairie ecosystem function0 aRelative effects of precipitation variability and warming on tal a3053 -30680 v83 a

Precipitation and temperature drive many aspects of terrestrial ecosystem function. Climate change scenarios predict increasing precipitation variability and temperature, and long term experiments are required to evaluate the ecosystem consequences of interannual climate variation, increased growing season (intra-annual) rainfall variability, and warming. We present results from an experiment applying increased growing season rainfall variability and year round warming in native tallgrass prairie. During ten years of study, total growing season rainfall varied 2-fold, and we found ~50–200% interannual variability in plant growth and aboveground net primary productivity (ANPP), leaf carbon assimilation (ACO2), and soil CO2 efflux (JCO2) despite only ~40% variation in mean volumetric soil water content (0–15 cm, Θ15). Interannual variation in soil moisture was thus amplified in most measures of ecosystem response. Differences between years in Θ15 explained the greatest portion (14–52%) of the variation in these processes. Experimentally increased intra-annual season rainfall variability doubled the amplitude of intra-annual soil moisture variation and reduced Θ15 by 15%, causing most ecosystem processes to decrease 8–40% in some or all years with increased rainfall variability compared to ambient rainfall timing, suggesting reduced ecosystem rainfall use efficiency. Warming treatments increased soil temperature at 5 cm depth, particularly during spring, fall, and winter. Warming advanced canopy green up in spring, increased winter JCO2, and reduced summer JCO2 and forb ANPP, suggesting that the effects of warming differed in cooler versus warmer parts of the year. We conclude that (1) major ecosystem processes in this grassland may be substantially altered by predicted changes in interannual climate variability, intra-annual rainfall variability, and temperature, (2) interannual climate variation was a larger source of variation in ecosystem function than intra-annual rainfall variability and warming, and (3) effects of increased growing season rainfall variability and warming were small, but ecologically important. The relative effects of these climate drivers are likely to vary for different ecosystem processes and in wetter or drier ecosystems.

1 aFay, P.A.1 aBlair, John, M.1 aSmith, M.D.1 aNippert, Jesse, B.1 aCarlisle, J.D.1 aKnapp, Alan, K. uhttps://www.biogeosciences.net/8/3053/2011/02698nas a2200241 4500008004100000245009200041210006900133300001300202490000700215520193900222653002002161653003002181653003202211653002302243100001702266700002002283700001702303700001802320700001602338700002002354700001602374856006602390 2010 eng d00aFire and grazing impacts on silica production and storage in grass dominated ecosystems0 aFire and grazing impacts on silica production and storage in gra a263 -2780 v973 a

Grassland ecosystems are an important terrestrial component of the global biogeochemical silicon cycle. Although the structure and ecological functioning of grasslands are strongly influenced by fire and grazing, the role of these key ecological drivers in the production and storage of silicon represents a significant knowledge gap, particularly since they are being altered worldwide by human activities. We evaluated the effects of fire and grazing on the range and variability of plant derived biogenic silica stored in plant biomass and soils by sampling plants and soils from long-term experimental plots with known fire and grazing histories. Overall, plants and soils from grazed sites in the South African ecosystems had up to 76 and 54% greater biogenic silica totals (kg ha−1), respectively, than grazed North American sites. In North American soils, the combination of grazing and annual fire resulted in the greatest abundance of biogenic silica, whereas South African soils had the highest biogenic silica content where grazed regardless of burn frequency. These results as well as those that show greater Si concentrations in grazed South African plants indicate that South African plants and soils responded somewhat differently to fire and grazing with respect to silicon cycling, which may be linked to differences in the evolutionary history and in the grazer diversity and grazing intensity of these ecosystems. We conclude that although fire and grazing (as interactive and/or independent factors) do not affect the concentration of Si taken up by plants, they do promote increased silicon storage in aboveground biomass and soil as a result of directly affecting other site factors such as aboveground net primary productivity. Therefore, as management practices, fire and grazing have important implications for assessing global change impacts on the terrestrial biogeochemical cycling of silicon.

10aBiogenic silica10aNorth American grasslands10aSoil South African savannas10aTerrestrial plants1 aMelzer, S.E.1 aKnapp, Alan, K.1 aFynn, R.W.S.1 aKirkman, K.P.1 aSmith, M.D.1 aBlair, John, M.1 aKelly, E.F. uhttps://link.springer.com/article/10.1007%2Fs10533-009-9371-302253nas a2200265 4500008004100000245013500041210006900176300001300245490000700258520141500265100001801680700001301698700001601711700001801727700001801745700001601763700001201779700001401791700002001805700001401825700002301839700001901862700001601881856009001897 2010 eng d00aVariation in gene expression of Andropogon gerardii in response to altered environmental conditions associated with climate change0 aVariation in gene expression of Andropogon gerardii in response  a374 -3830 v983 a

1. If we are to understand the mechanisms underlying species responses to climate change in natural systems, studies are needed that focus on responses of non-model species under field conditions. We measured transcriptional profiles of individuals of Andropogon gerardii, a C4 grass native to North American grasslands, in a field experiment in which both temperature and precipitation were manipulated to simulate key aspects of forecasted climate change. 2. By using microarrays developed for a closely related model species, Zea mays, we were able to compare the relative influence of warming versus altered soil moisture availability on expression levels of over 7000 genes, identify responsive functional groups of genes and correlate changes in gene transcription with physiological responses. 3. We observed more statistically significant shifts in transcription levels of genes in response to thermal stress than in response to water stress. We also identified candidate genes that demonstrated transcription levels closely associated with physiological variables, in particular chlorophyll fluorescence. 4.Synthesis. These results suggest that an ecologically important species responds differently to different environmental aspects of forecast climate change. These translational changes have the potential to influence phenotypic characters and ultimately adaptive responses.

1 aTravers, S.E.1 aTang, Z.1 aCaragea, D.1 aGarrett, K.A.1 aHulbert, S.H.1 aLeach, J.E.1 aBai, J.1 aSaleh, A.1 aKnapp, Alan, K.1 aFay, P.A.1 aNippert, Jesse, B.1 aSchnable, P.S.1 aSmith, M.D. uhttps://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2745.2009.01618.x02607nas a2200325 4500008004100000245011200041210006900153300001300222490000700235520168300242653000901925653000901934653001501943653001201958653001301970653001301983100001501996700002002011700002002031700001602051700002202067700001602089700002402105700001702129700001702146700001602163700001602179700002002195856006602215 2009 eng d00aControls of aboveground net primary production in mesic savanna grasslands: An inter-hemispheric comparison0 aControls of aboveground net primary production in mesic savanna  a982 -9950 v123 a

Patterns and controls of annual aboveground net primary productivity (ANPP) are fundamental metrics of ecosystem functioning. It is generally assumed, but rarely tested, that determinants of ANPP in one region within a biome will operate similarly throughout that biome, as long as physiognomy and climate are broadly consistent. We tested this assumption by quantifying ANPP responses to fire, grazing history, and nitrogen (N) addition in North American (NA) and South African (SA) savanna grasslands. We found that total ANPP responded in generally consistent ways to fire, grazing history, and N addition on both continents. Annual fire in both NA and SA consistently stimulated total ANPP (28–100%) relative to unburned treatments at sites with deep soils, and had no effect on ANPP in sites with shallow soils. Fire did not affect total ANPP in sites with a recent history of grazing, regardless of whether a single or a diverse suite of large herbivores was present. N addition interacted strongly and consistently with fire regime in both NA and SA. In annually burned sites that were not grazed, total ANPP was stimulated by N addition (29–39%), but there was no effect of N fertilization in the absence of fire. In contrast, responses in forb ANPP to fire and grazing were somewhat divergent across this biome. Annual fire in NA reduced forb ANPP, whereas grazing increased forb ANPP, but neither response was evident in SA. Thus, despite a consistent response in total ANPP, divergent responses in forb ANPP suggest that other aspects of community structure and ecosystem functioning differ in important ways between these mesic savanna grasslands.

10aANPP10afire10aGrasslands10aGrazing10anitrogen10aSavannas1 aBuis, G.M.1 aBlair, John, M.1 aBurkepile, D.E.1 aBurns, C.E.1 aChamberlain, A.J.1 aChapman, P.1 aCollins, Scott., L.1 aFynn, R.W.S.1 aGovender, N.1 aKirkman, K.1 aSmith, M.D.1 aKnapp, Alan, K. uhttps://link.springer.com/article/10.1007%2Fs10021-009-9273-102307nas a2200241 4500008004100000245010400041210006900145300001300214490000700227520153700234653002401771653002401795653002201819653001001841653001601851653002301867100002301890700001401913700001901927700002001946700001601966856008301982 2009 eng d00aEcophysiological responses of two dominant grasses to altered temperature and precipitation regimes0 aEcophysiological responses of two dominant grasses to altered te a400 -4080 v353 a

Ecosystem responses to climate change will largely be driven by responses of the dominant species. However, if co-dominant species have traits that lead them to differential responses, then predicting how ecosystem structure and function will be altered is more challenging. We assessed differences in response to climate change factors for the two dominant C4 grass species in tallgrass prairie, Andropogon gerardii and Sorghastrum nutans, by measuring changes in a suite of plant ecophysiological traits in response to experimentally elevated air temperatures and increased precipitation variability over two growing seasons. Maximum photosynthetic rates, stomatal conductance, water-use efficiency, chlorophyll fluorescence, and leaf water potential varied with leaf and canopy temperature as well as with volumetric soil water content (0–15 cm). Both species had similar responses to imposed changes in temperature and water availability, but when differences occurred, responses by A. gerardii were more closely linked with changes in air temperature whereas S. nutans was more sensitive to changes in water availability. Moreover, S. nutans was more responsive overall than A. gerardii to climate alterations. These results indicate both grass species are responsive to forecast changes in temperature and precipitation, but their differential sensitivity to temperature and water availability suggest that future population and community structure may vary based on the magnitude and scope of an altered climate.

10aAndropogon gerardii10aClimate variability10aLeaf gas exchange10aRaMPs10aSensitivity10aSorghastrum nutans1 aNippert, Jesse, B.1 aFay, P.A.1 aCarlisle, J.D.1 aKnapp, Alan, K.1 aSmith, M.D. uhttps://www.sciencedirect.com/science/article/pii/S1146609X09000204?via%3Dihub02353nas a2200145 4500008004100000245011800041210006900159300001500228490000700243520182300250100001602073700002002089700002402109856007402133 2009 eng d00aA framework for assessing ecosystem dynamics in response to chronic resource alterations induced by global change0 aframework for assessing ecosystem dynamics in response to chroni a3279 -32890 v903 a

In contrast to pulses in resource availability following disturbance events, many of the most pressing global changes, such as elevated atmospheric carbon dioxide concentrations and nitrogen deposition, lead to chronic and often cumulative alterations in available resources. Therefore, predicting ecological responses to these chronic resource alterations will require the modification of existing disturbance-based frameworks. Here, we present a conceptual framework for assessing the nature and pace of ecological change under chronic resource alterations. The “hierarchical-response framework” (HRF) links well-documented, ecological mechanisms of change to provide a theoretical basis for testing hypotheses to explain the dynamics and differential sensitivity of ecosystems to chronic resource alterations. The HRF is based on a temporal hierarchy of mechanisms and responses beginning with individual (physiological/metabolic) responses, followed by species reordering within communities, and finally species loss and immigration. Each mechanism is hypothesized to differ in the magnitude and rate of its effects on ecosystem structure and function, with this variation depending on ecosystem attributes, such as longevity of dominant species, rates of biogeochemical cycling, levels of biodiversity, and trophic complexity. Overall, the HRF predicts nonlinear changes in ecosystem dynamics, with the expectation that interactions with natural disturbances and other global-change drivers will further alter the nature and pace of change. The HRF is explicitly comparative to better understand differential sensitivities of ecosystems, and it can be used to guide the design of coordinated, cross-site experiments to enable more robust forecasts of contemporary and future ecosystem dynamics.

1 aSmith, M.D.1 aKnapp, Alan, K.1 aCollins, Scott., L. uhttps://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/08-1815.102018nas a2200229 4500008004100000245009000041210006900131300001300200490000800213520133600221653002901557653001401586653001701600653001601617653001501633100001201648700001501660700001801675700001301693700001601706856006601722 2008 eng d00aComparison of damage to native and exotic tallgrass prairie plants by natural enemies0 aComparison of damage to native and exotic tallgrass prairie plan a197 -2100 v1983 a

We surveyed the prevalence and amount of leaf damage related to herbivory and pathogens on 12 pairs of exotic (invasive and noninvasive) and ecologically similar native plant species in tallgrass prairie to examine whether patterns of damage match predictions from the enemy release hypothesis. We also assessed whether natural enemy impacts differed in response to key environmental factors in tallgrass prairie by surveying the prevalence of rust on the dominant C4 grass, Andropogon gerardii, and its congeneric invasive exotic C4 grass, A. bladhii, in response to fire and nitrogen fertilization treatments. Overall, we found that the native species sustain 56.4% more overall leaf damage and 83.6% more herbivore-related leaf damage when compared to the exotic species. Moreover, we found that the invasive exotic species sustained less damage from enemies relative to their corresponding native species than the noninvasive exotic species. Finally, we found that burning and nitrogen fertilization both significantly increased the prevalence of rust fungi in the native grass, while rust fungi rarely occurred on the exotic grass. These results indicate that reduced damage from enemies may in part explain the successful naturalization of exotic species and the spread of invasive exotic species in tallgrass prairie.

10aEnemy release hypothesis10agrassland10aInvasiveness10aLeaf damage10aRust fungi1 aHan, X.1 aDend, S.P.1 aGarrett, K.A.1 aFang, L.1 aSmith, M.D. uhttps://link.springer.com/article/10.1007%2Fs11258-008-9395-002231nas a2200349 4500008004100000245008200041210006900123300001300192490000700205520128800212653001901500653001201519653001501531653001801546653001501564100002001579700001401599700001701613700001801630700001201648700001901660700001601679700001601695700001501711700001401726700001801740700001701758700001501775700001401790700001301804856006401817 2008 eng d00aConsequences of more extreme precipitation regimes for terrestrial ecosystems0 aConsequences of more extreme precipitation regimes for terrestri a811 -8210 v583 a

mplification of the hydrological cycle as a consequence of global warming is forecast to lead to more extreme intra-annual precipitation regimes characterized by larger rainfall events and longer intervals between events. We present a conceptual framework, based on past investigations and ecological theory, for predicting the consequences of this underappreciated aspect of climate change. We consider a broad range of terrestrial ecosystems that vary in their overall water balance. More extreme rainfall regimes are expected to increase the duration and severity of soil water stress in mesic ecosystems as intervals between rainfall events increase. In contrast, xeric ecosystems may exhibit the opposite response to extreme events. Larger but less frequent rainfall events may result in proportional reductions in evaporative losses in xeric systems, and thus may lead to greater soil water availability. Hydric (wetland) ecosystems are predicted to experience reduced periods of anoxia in response to prolonged intervals between rainfall events. Understanding these contingent effects of ecosystem water balance is necessary for predicting how more extreme precipitation regimes will modify ecosystem processes and alter interactions with related global change drivers.

10aClimate change10aDrought10aEcosystems10aPrecipitation10asoil water1 aKnapp, Alan, K.1 aBeier, C.1 aBriske, D.D.1 aClassen, A.T.1 aLuo, Y.1 aReichstein, M.1 aSmith, M.D.1 aSmith, S.D.1 aBell, J.E.1 aFay, P.A.1 aHeisler, J.L.1 aLeavitt, S.W1 aSherry, R.1 aSmith, B.1 aWeng, E. uhttps://academic.oup.com/bioscience/article/58/9/811/25085302031nas a2200229 4500008004100000245011400041210006900155260002400224300001300248520129100261100002001552700001901572700001901591700001501610700001801625700001501643700002001658700001901678700001601697700002001713856006801733 2008 eng d00aEcological consequences of the replacement of native grassland by Juniperus virginiana and other woody plants0 aEcological consequences of the replacement of native grassland b bSpringer-Verlag, NY a156 -1693 a

Although grasslands have been altered by humans for thousands of years (Wedel 1961; Bond et al. 2003), the loss of grassland as a result of anthropogenic activities has increased dramatically over the past 150 years. When Europeans first settled the Midwest and Great Plains, the greatest threat to native grasslands was the conversion of the most highly productive of these ecosystems to row-crop agriculture (Samson and Knopf 1994). Later, with improvements in soil moisture management and irrigation technology, even low-productivity grasslands were plowed. Today, those remnants of the most productive grasslands that escaped the plow are threatened, as are most of Earth’s ecosystems, by a variety of global change phenomena (Vitousek et al. 1997), with the invasion and expansion of woody species into grasslands one of the greatest of these threats. The replacement of grasslands by shrubland, woodland, and forest is a concern not only in the United States but worldwide (Archer et al. 1988; Van Auken 2000; Roques et al. 2001; Silva et al. 2001). Species of woody plants that invade grasslands may include both native plants which previously existed as more minor components of the ecosystem as well as alien species (Bragg and Hulbert 1976; Harcombe et al. 1993).

1 aKnapp, Alan, K.1 aMcCarron, J.K.1 aSilletti, A.M.1 aHoch, G.A.1 aHeisler, J.L.1 aLett, M.S.1 aBlair, John, M.1 aBriggs, J., M.1 aSmith, M.D.1 aVan Auken, O.W. uhttps://link.springer.com/chapter/10.1007%2F978-0-387-34003-6_802483nas a2200157 4500008004100000245014000041210006900181300001300250490000800263520190200271100001502173700002002188700001602208700002402224856007702248 2008 eng d00aInfluence of grazing and fire frequency on small-scale plant community structure and resource variability in native tallgrass prairie0 aInfluence of grazing and fire frequency on smallscale plant comm a859 -8660 v1173 a

In grasslands worldwide, grazing by ungulates and periodic fires are important forces affecting resource availability and plant community structure. It is not clear, however, whether changes in community structure are the direct effects of the disturbance (i.e. fire and grazing) or are mediated indirectly through changes in resource abundance and availability. In North American tallgrass prairies, fire and grazing often have disparate effects on plant resources and plant diversity, yet, little is known about the individual and interactive effects of fire and grazing on resource variability and how that variability relates to heterogeneity in plant community structure, particularly at small scales. We conducted a field study to determine the interactive effects of different long-term fire regimes (annual vs four-year fire frequency) and grazing by native ungulates (Bos bison) on small-scale plant community structure and resource variability (N and light) in native tallgrass prairie. Grazing enhanced light and nitrogen availability, but did not affect small-scale resource variability. In addition, grazing reduced the dominance of C4 grasses which enhanced species richness, diversity and community heterogeneity. In contrast, annual fire increased community dominance and reduced species richness and diversity, particularly in the absence of grazing, but had no effect on community heterogeneity, resource availability and resource variability. Variability in the abundance of resources showed no relationship with community heterogeneity at the scale measured in this study, however we found a relationship between community dominance and heterogeneity. Therefore, we conclude that grazing generated small-scale community heterogeneity in this mesic grassland by directly affecting plant community dominance, rather than indirectly through changes in resource variability.

1 aVeen, G.F.1 aBlair, John, M.1 aSmith, M.D.1 aCollins, Scott., L. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/j.0030-1299.2008.16515.x01991nas a2200265 4500008004100000245007900041210006900120300001300189490000700202520119800209100001601407700001901423700001601442700001701458700001901475700001401494700001501508700001701523700001501540700001701555700001401572700001601586700001701602856010601619 2007 eng d00aDoes species diversity limitproductivity in natural grassland communities?0 aDoes species diversity limitproductivity in natural grassland co a680 -6890 v103 aTheoretical analyses and experimental studies of synthesized assemblages indicate that under particular circumstances species diversity can enhance community productivity through niche complementarity. It remains unclear whether this process has important effects in mature natural ecosystems where competitive feedbacks and complex environmental influences affect diversity–productivity relationships. In this study, we evaluated diversity–productivity relationships while statistically controlling for environmental influences in 12 natural grassland ecosystems. Because diversity–productivity relationships are conspicuously nonlinear, we developed a nonlinear structural equation modeling (SEM) methodology to separate the effects of diversity on productivity from the effects of productivity on diversity. Meta-analysis was used to summarize the SEM findings across studies. While competitive effects were readily detected, enhancement of production by diversity was not. These results suggest that the influence of small-scale diversity on productivity in mature natural systems is a weak force, both in absolute terms and relative to the effects of other controls on productivity.1 aGrace, J.B.1 aAnderson, T.M.1 aSmith, M.D.1 aSeabloom, E.1 aAndelman, S.J.1 aMeche, G.1 aWeiher, E.1 aAllain, L.K.1 aJutila, H.1 aSankaran, M.1 aKnops, J.1 aRitchie, M.1 aWhiles, M.R. uhttp://knz.lternet.edu/content/does-species-diversity-limitproductivity-natural-grassland-communities02177nas a2200241 4500008004100000245014800041210006900189300001100258490000600269520134800275100001801623700001601641700001201657700001801669700001601687700001901703700002001722700001901742700001401761700001401775700001801789856012801807 2007 eng d00aEcological genomics: making the leap from model systems in the lab to native populations in the field. Frontiers in Ecology and the Environment0 aEcological genomics making the leap from model systems in the la a19 -240 v53 aRecent reviews have emphasized the need to incorporate genomics into ecological field studies to further understand how species respond to changing environmental conditions. Genomic tools, such as cDNA (complementary DNA) microarrays, allow for the simultaneous analysis of gene expression of thousands of genes from all or part of an organism's genome (the transcription profile), thereby revealing the genetic mechanisms that underlie species' responses to environmental change. However, despite their potential, two major limitations have hindered the incorporation of microarrays and other genomic tools into field studies: (1) the limited availability of microarrays for ecologically relevant, non-model species and limited financial resources for developing new microarrays; and (2) concern that high sensitivity of gene expression to even subtle alterations in environmental conditions will hinder detection of relevant changes in field measures of transcription profiles. Here, we show that with cross-species hybridizations of microarrays developed for a closely related model organism, an appropriate experimental design, and sufficient replication, transcriptional profiling can successfully be incorporated into field studies. In this way, relevant changes in gene expression with changing environmental conditions can be detected.1 aTravers, S.E.1 aSmith, M.D.1 aBai, J.1 aHulbert, S.H.1 aLeach, J.E.1 aSchnable, P.S.1 aKnapp, Alan, K.1 aMilliken, G.A.1 aFay, P.A.1 aSaleh, A.1 aGarrett, K.A. uhttp://knz.lternet.edu/content/ecological-genomics-making-leap-model-systems-lab-native-populations-field-frontiers-ecology02989nas a2200241 4500008004100000245012400041210006900165300001300234490000800247520216100255653001202416653002502428653002702453653001802480653001802498100002002516700001602536700001702552700001802569700001702587700001602604856012702620 2006 eng d00aConvergence and contingency in production-precipitation relationships in North American and South African C4 grasslands0 aConvergence and contingency in productionprecipitation relations a456 -4640 v1493 aMesic grasslands in North America and South Africa share many structural attributes, but less is known of their functional similarities. We assessed the control of a key ecosystem process, aboveground net primary production (ANPP), by interannual variation in precipitation amount and pattern via analysis of data sets (15- and 24-year periods) from long-term research programs on each continent. Both sites were dominated by C4 grasses and had similar growing season climates; thus, we expected convergence in precipitation–ANPP relationships. Lack of convergence, however, would support an alternative hypothesis—that differences in evolutionary history and purportedly greater climatic variability in South Africa fundamentally alter the functioning of southern versus northern hemisphere grasslands. Neither mean annual precipitation nor mean ANPP differed between the South African and North American sites (838 vs. 857 mm/year, 423.5 vs. 461.4 g/m2 respectively) and growing season precipitation–ANPP relationships were similar. Despite overall convergence, there were differences between sites in how the seasonal timing of precipitation affected ANPP. In particular, interannual variability in precipitation that fell during the first half of the growing season strongly affected annual ANPP in South Africa (P < 0.01), but was not related to ANPP in North America (P = 0.098). Both sites were affected similarly by late season precipitation. Divergence in the seasonal course of available soil moisture (chronically low in the winter and early spring in the South African site vs. high in the North American site) is proposed as a key contingent factor explaining differential sensitivity in ANPP to early season precipitation in these two grasslands. These long-term data sets provided no support for greater rainfall, temperature or ANPP variability in the South African versus the North American site. However, greater sensitivity of ANPP to early season precipitation in the South African grassland suggests that future patterns of productivity may be more responsive to seasonal changes in climate compared with the North American site.10aclimate10aEvolutionary history10aNet primary production10aPrecipitation10asoil moisture1 aKnapp, Alan, K.1 aBurns, C.E.1 aFynn, R.W.S.1 aKirkman, K.P.1 aMorris, C.D.1 aSmith, M.D. uhttp://knz.lternet.edu/content/convergence-and-contingency-production-precipitation-relationships-north-american-and-south02104nas a2200229 4500008004100000245008300041210006900124300001500193490000800208520135300216653002401569653002301593653001901616653001801635653001901653653002301672653001701695100001801712700002001730700001601750856010801766 2006 eng d00aGrowth responses of twodominant C4 grass species to altered water availability0 aGrowth responses of twodominant C4 grass species to altered wate a1001 -10100 v1673 aIdentifying key ecophysiological traits that differ among dominant plant species and can be linked to species‐specific responses to drought would improve our ability to forecast community and ecosystem responses to global climate change. The mesic grasslands of the central plains of North America are dominated by two C4 grass species, Andropogon gerardii and Sorghastrum nutans, which purportedly differ in their tolerance of water stress. Individuals of these two species were grown in the field under rain‐out shelters and subjected to wet (watered every 2–3 d) or dry (repeatedly subjected to wilting before watering) soil moisture regimes. A range of ecophysiological traits potentially important for tolerating water stress were concurrently measured. Although few traits differed between the species in the wet treatment, several traits were identified in the dry treatment that may enable A. gerardii to better tolerate drought. These were greater allocation to roots, reduced allocation to flowering, more rapid leaf turnover, and more rapid recovery of photosynthesis after wilting. The latter two traits may be particularly important for coping with increased variability in rainfall regimes in the future and are consistent with recently documented responses of A. gerardii to experimental increases in soil moisture variability.10aAndropogon gerardii10abiomass allocation10aClimate change10aleaf turnover10aphotosynthesis10aSorghastrum nutans10awater stress1 aSwemmer, A.M.1 aKnapp, Alan, K.1 aSmith, M.D. uhttp://knz.lternet.edu/content/growth-responses-twodominant-c4-grass-species-altered-water-availability02600nas a2200133 4500008004100000245009900041210006900140300001500209490000700224520207400231100002402305700001602329856012102345 2006 eng d00aScale-dependent interaction of fire andgrazing on community heterogeneity in tallgrass prairie0 aScaledependent interaction of fire andgrazing on community heter a2058 -20670 v873 aNatural disturbances affect spatial and temporal heterogeneity in plant communities, but effects vary depending on type of disturbance and scale of analysis. In this study, we examined the effects of fire frequency (1-, 4-, and 20-yr intervals) and grazing by bison on spatial and temporal heterogeneity in species composition in tallgrass prairie plant communities. Compositional heterogeneity was estimated at 10-, 50-, and 200-m2 scales. For each measurement scale, we used the average Euclidean Distance (ED) between samples within a year (2000) to measure spatial heterogeneity and between all time steps (1993–2000) for each sample to measure temporal heterogeneity. The main effects of fire and grazing were scale independent. Spatial and temporal heterogeneity were lowest on annually burned sites and highest on infrequently burned (20-yr) sites at all scales. Grazing reduced spatial heterogeneity and increased temporal heterogeneity at all scales. The rate of community change over time decreased as fire frequency increased at all scales, whereas grazing had no effect on rate of community change over time at any spatial scale. The interactive effects of fire and grazing on spatial and temporal heterogeneity differed with scale. At the 10-m2 scale, grazing increased spatial heterogeneity in annually burned grassland but decreased heterogeneity in less frequently burned areas. At the 50-m2 scale, grazing decreased spatial heterogeneity on 4-yr burns but had no effect at other fire frequencies. At the 10-m2 scale, grazing increased temporal heterogeneity only on 1- and 20-yr burn sites. Our results show that the individual effects of fire and grazing on spatial and temporal heterogeneity in mesic prairie are scale independent, but the interactive effects of these disturbances on community heterogeneity change with scale of measurement. These patterns reflect the homogenizing impact of fire at all spatial scales, and the different frequency, intensity, and scale of patch grazing by bison in frequently burned vs. infrequently burned areas.1 aCollins, Scott., L.1 aSmith, M.D. uhttp://knz.lternet.edu/content/scale-dependent-interaction-fire-andgrazing-community-heterogeneity-tallgrass-prairie03530nas a2200301 4500008004100000245008000041210006900121300001300190490000700203520263500210653001102845653001702856653001802873653001402891653001802905653002702923653001302950653001602963653001802979653002402997653002003021100001703041700002003058700001903078700001503097700001603112856010003128 2005 eng d00aIndicators of plant species richness in AVIRIS spectra of a mesic grassland0 aIndicators of plant species richness in AVIRIS spectra of a mesi a304 -3160 v983 aHyperspectral imagery of the Konza Prairie Biological Station in northeastern Kansas was used to evaluate upwelling spectral radiance, prairie spectral reflectance and band ratios of each as potential indicators of vascular plant species richness in a mesic grassland. The extent to which spatial variability in these parameters related to plant species richness also was investigated. A 224 channel hyperspectral data cube acquired in June 2000 by the Airborne Visible and Infrared Imaging Spectrometer (AVIRIS) provided complete coverage of the 400–2500 nm range at approximately 10 nm per channel. After band deletions accounted for detector overlap and strong atmospheric attenuation features, 176 bands were retained for analysis and spanned the 404–2400 nm range. Prairie reflectance was estimated via radiative transfer modeling and scaling to a library spectrum of highway construction material. Data were sampled from pixels having a 19 m ground sample distance (GSD) to represent each of 93 vegetation sampling transects. Reflectance and radiance at mid-infrared wavelengths (e.g., 1553 nm), and band ratios that were based on atmospheric windows in the red, near-infrared and mid-infrared spectra estimated species richness to within 6 to 7 species per transect. The 856 to 780 nm radiance or reflectance ratio yielded maximum adjusted coefficients of determination (r2) of approximately 0.4 in regressions with richness when data from bison-grazed and ungrazed areas were combined. These regressions remained significant (p ≤ 0.001) when only ungrazed areas were assessed although r2 reduced to approximately 0.2. Richness was related significantly also to the 433 to 674 nm reflectance ratio for grazed-plus-ungrazed and ungrazed-only areas. In contrast, the effectiveness of the 433 to 674 nm radiance ratio was reduced by atmospheric backscatter. Species richness did not correlate strongly or consistently with transect spatial variability (coefficient of variation or range) in radiance, reflectance or band ratio value, apparently as a consequence of the relatively small area sampled for each transect (approximately 0.5 ha). Relationships between richness and prairie spectral features were explained by the influence of soil exposure on both parameters. Richness and estimated soil exposure tended to increase from ungrazed lowlands, to ungrazed slopes, to ungrazed uplands to grazed areas. Remotely sensed estimates of soil exposure may be particularly useful in addressing plant species richness on grazed grasslands owing to an overall similarity in spectral reflectance among dominant plant species.10aAVIRIS10aBiodiversity10aBison grazing10agrassland10aHyperspectral10aPlant species richness10aRadiance10aReflectance10aSoil exposure10aSpatial variability10aSpectral mixing1 aCarter, G.A.1 aKnapp, Alan, K.1 aAnderson, J.E.1 aHoch, G.A.1 aSmith, M.D. uhttp://knz.lternet.edu/content/indicators-plant-species-richness-aviris-spectra-mesic-grassland02169nas a2200145 4500008004100000245006000041210005800101300001500159490000700174520170900181100001701890700001701907700001601924856008301940 2005 eng d00aA test for community change using a null model approach0 atest for community change using a null model approach a1761 -17710 v153 aQuantifying patterns of temporal or spatial change in community structure is critical for assessing the impact of disturbances on biological systems and the stability of ecosystems. Detecting change in communities can be problematic, however, because of the inherent variability of systems and limitations of commonly used methods, such as similarity indices and ordination that do not explicitly test a hypothesis. Here we present empirical data to show a strong relationship between species mean abundance and variability across three broad taxonomic groups (plants, zooplankton, and fish). These statistical relationships were then used to construct null models of expected community variability that were used to test against the observed temporal change of these communities. We evaluated the ability of this approach to detect significant temporal change above that associated with random variation with nine communities (three Midwestern stream fish, three north temperate zooplankton, and three tallgrass prairie plant), each having long-term data sets and different expected levels of change. Nonrandom change was detected in 21.3% of samples from the expected low-change communities, 52.6% in moderately changed communities, and 60.4% in high-change communities. Thus, this approach was effective in detecting change over time in those communities expected to change most. By using empirical relationships between species abundance and variability, this null model approach provides ecologists and resource managers an objective tool, which can be used along with existing community indices and statistical techniques to assess the type and magnitude of community change with limited data sets.1 aSchaefer, J.1 aGido, K., B.1 aSmith, M.D. uhttp://knz.lternet.edu/content/test-community-change-using-null-model-approach00882nas a2200313 4500008004100000245006200041210006100103300001300164490000800177100001700185700001600202700001400218700002000232700001500252700001500267700001600282700001700298700001400315700001800329700001800347700001500365700001700380700001400397700001500411700001900426700001600445700001900461856008800480 2004 eng d00aConvergence across biomes to a common rain-use efficiency0 aConvergence across biomes to a common rainuse efficiency a651 -6540 v4291 aHuxman, T.E.1 aSmith, M.D.1 aFay, P.A.1 aKnapp, Alan, K.1 aShaw, M.R.1 aLoik, M.E.1 aSmith, S.D.1 aTissue, D.T.1 aZak, J.C.1 aWeltzin, J.F.1 aPockman, W.T.1 aSala, O.E.1 aHaddad, B.M.1 aHarte, J.1 aKoch, G.W.1 aSchwinning, S.1 aSmall, E.E.1 aWilliams, D.G. uhttp://knz.lternet.edu/content/convergence-across-biomes-common-rain-use-efficiency02301nas a2200157 4500008004100000245007300041210006900114300001300183490000800196520177300204100001601977700001501993700001402008700002002022856010102042 2004 eng d00aDominance not diversity determines invasibility of tallgrass prairie0 aDominance not diversity determines invasibility of tallgrass pra a253 -2620 v1063 aMany recent studies suggest that more diverse communities are more resistant to invasion. Community characteristics that most strongly influence invasion are uncertain, however, due to covariation of diversity with competition and crowding. We examined separately the effects of species richness and dominance on invasion by an exotic legume, Melilotus officinalis, in intact, native Kansas grassland. We manipulated dominance of C4 grasses by reducing their abundance (i.e. ramet densities) by ∼25 and 50%. In addition, richness was reduced by removing species that were mainly rare and uncommon as might be expected with environmental changes such as drought and fragmentation. In both years of the study (2001–2002), invasibility, measured as peak establishment of Melilotus, was not affected by a 3-fold reduction in species richness, nor was there an interaction between loss of species and reduced dominance on invasion. In contrast, reductions in abundance of the dominants significantly reduced invasibility of the grassland plots in both years. Because the abundance of dominants was highly correlated with measures of competition (i.e. ratio of dominant biomass to total biomass) and crowding (total stem densities), this pattern was opposite to that expected if competition were indeed limiting invasion. Rather, invasion appeared to be facilitated by the dominant species, most likely because reduced dominance increased environmental stress. Our results suggest that dominance is the key community characteristic determining invasibility, because highly competitive and space-filling species can either enhance or reduce susceptibility to invasion depending on whether dominants create a more competitive environment or alleviate stressful conditions.1 aSmith, M.D.1 aWilcox, J.1 aKelly, T.1 aKnapp, Alan, K. uhttp://knz.lternet.edu/content/dominance-not-diversity-determines-invasibility-tallgrass-prairie01950nas a2200241 4500008004100000245009200041210006900133300001300202490000600215520117800221100002001399700001601419700002401435700001701459700001301476700001601489700001501505700002401520700001401544700001501558700001901573856011601592 2004 eng d00aGenerality in ecology: testing North American grassland rules in South African savannas0 aGenerality in ecology testing North American grassland rules in  a483 -4910 v93 aEcology has emerged as a global science, and there is a pressing need to identify ecological rules – general principles that will improve its predictive capability for scientists and its usefulness for managers and policy makers. Ideally, the generality and limits of these ecological rules should be assessed using extensive, coordinated experiments that ensure consistency in design and comparability of data. To improve the design of these large-scale efforts, existing data should be used to test prospective ecological rules and to identify their limits and contingencies. As an example of this approach, we describe prospective rules for grassland responses to fire and rainfall gradients, identified from long-term studies of North American grasslands and tested with existing data from long-term experiments in South African savanna grasslands. Analyses indicated consistent effects of fire on the abundance of the dominant (grasses) and subdominant (forbs) flora on both continents, but no common response of grass or forb abundance across a rainfall gradient. Such analyses can inform future research designs to refine and more explicitly test ecological rules.1 aKnapp, Alan, K.1 aSmith, M.D.1 aCollins, Scott., L.1 aZambatis, N.1 aPeel, M.1 aEmery, S.M.1 aWojdak, J.1 aHorner-Devine, M.C.1 aBiggs, H.1 aKruger, J.1 aAndelman, S.J. uhttp://knz.lternet.edu/content/generality-ecology-testing-north-american-grassland-rules-south-african-savannas01899nas a2200229 4500008004100000245014600041210006900187300001300256490000600269520109500275100001801370700001601388700001901404700001501423700001701438700002401455700001601479700001601495700001901511700002101530856011801551 2004 eng d00aInvasion in space and time: non-native species richness and relative abundance respond to interannual variation in productivity and diversity0 aInvasion in space and time nonnative species richness and relati a947 -9570 v73 aEcologists have long sought to understand the relationships among species diversity, community productivity and invasion by non-native species. Here, four long-term observational datasets were analyzed using repeated measures statistics to determine how plant species richness and community resource capture (i.e. productivity) influenced invasion. Multiple factors influenced the results, including the metric used to quantify invasion, interannual variation and spatial scale. Native richness was positively correlated with non-native richness, but was usually negatively correlated with non-native abundance, and these patterns were stronger at the larger spatial scale. Logistic regressions indicated that the probability of invasion was reduced both within and following years with high productivity, except at the desert grassland site where high productivity was associated with increased invasion. Our analysis suggests that while non-natives were most likely to establish in species rich communities, their success was diminished by high resource capture by the resident community.1 aCleland, E.E.1 aSmith, M.D.1 aAndelman, S.J.1 aBowles, C.1 aCarney, K.M.1 aHorner-Devine, M.C.1 aDrake, J.M.1 aEmery, S.M.1 aGramling, J.M.1 aVandermast, D.B. uhttp://knz.lternet.edu/content/invasion-space-and-time-non-native-species-richness-and-relative-abundance-respond02695nas a2200157 4500008004100000245012600041210006900167300001500236490000700251520208300258100002002341700001902361700001602380700001702396856012402413 2004 eng d00aScale dependence in the relationship between species richness and productivity: the role of spatial and temporal turnover0 aScale dependence in the relationship between species richness an a2701 -27080 v853 aRecent research in aquatic systems suggests that productivity–richness relationships change with spatial scale and that species turnover (i.e., spatial and temporal variation in species composition) plays an important role in generating this scale dependence. The generality of such scale dependence and the effects of variation in temporal scale remain unknown. We examined the extent to which the richness–productivity relationship in terrestrial plant communities depends on spatial or temporal scale and evaluated how spatial and temporal turnover (i.e., species turnover in space and time) generates scale dependence in these relationships using data from two Long-Term Ecological Research (LTER) sites (Jornada and Konza). We found a weak hump-shaped relationship (Jornada) and no relationship (Konza) between richness and productivity at the smallest focal scale (1 m2 at Jornada and 50 m2 at Konza) at each site, but strong hump-shaped relationships at the largest focal scale (49 m2 at Jornada and 200 m2 at Konza) for each site. Relationships between spatial turnover and productivity at each site mirrored the productivity–richness relationships that emerged at the larger spatial scale (i.e., a significant hump-shaped pattern). In contrast, temporal turnover was unrelated to productivity, and hence increasing temporal scale did not appreciably change the form of the productivity–richness relationship. Our study suggests that the way in which productivity–richness relationships change with spatial or temporal scale depends on the form and strength of the underlying relationship between species turnover and productivity. Moreover, we contend that a dominant effect of increasing productivity is the generation of dissimilarity in species composition among localities that comprise a region, rather than increasing the number of species that occur within local communities. Thus, understanding the mechanisms that cause species turnover to vary with productivity is critical to understanding scale dependence in richness–productivity relationships.1 aChalcraft, D.R.1 aWilliams, J.W.1 aSmith, M.D.1 aWhiles, M.R. uhttp://knz.lternet.edu/content/scale-dependence-relationship-between-species-richness-and-productivity-role-spatial-and02258nas a2200361 4500008004100000245009100041210006900132300001300201490000700214520122700221653001401448653001401462653001801476653001801494653001801512100001801530700001501548700001901563700001901582700001401601700001501615700001401630700001701644700002001661700001201681700001801693700001501711700001401726700001601740700001701756700001401773856010901787 2003 eng d00aAssessing the response of terrestrial ecosystems to potential changes in precipitation0 aAssessing the response of terrestrial ecosystems to potential ch a941 -9520 v533 aChanges in Earth's surface temperatures caused by anthropogenic emissions of greenhouse gases are expected to affect global and regional precipitation regimes. Interactions between changing precipitation regimes and other aspects of global change are likely to affect natural and managed terrestrial ecosystems as well as human society. Although much recent research has focused on assessing the responses of terrestrial ecosystems to rising carbon dioxide or temperature, relatively little research has focused on understanding how ecosystems respond to changes in precipitation regimes. Here we review predicted changes in global and regional precipitation regimes, outline the consequences of precipitation change for natural ecosystems and human activities, and discuss approaches to improving understanding of ecosystem responses to changing precipitation. Further, we introduce the Precipitation and Ecosystem Change Research Network (PrecipNet), a new interdisciplinary research network assembled to encourage and foster communication and collaboration across research groups with common interests in the impacts of global change on precipitation regimes, ecosystem structure and function, and the human enterprise.10aCommunity10aecosystem10aglobal change10aPrecipitation10asoil moisture1 aWeltzin, J.F.1 aLoik, M.E.1 aSchwinning, S.1 aWilliams, D.G.1 aFay, P.A.1 aHaddad, B.1 aHarte, J.1 aHuxman, T.E.1 aKnapp, Alan, K.1 aLin, G.1 aPockman, W.T.1 aShaw, M.R.1 aSmall, E.1 aSmith, M.D.1 aTissue, D.T.1 aZak, J.C. uhttp://knz.lternet.edu/content/assessing-response-terrestrial-ecosystems-potential-changes-precipitation01942nas a2200133 4500008004100000245007800041210006900119300001300188490000600201520146100207100001601668700002001684856010401704 2003 eng d00aDominant species maintain ecosystem function with non-random species loss0 aDominant species maintain ecosystem function with nonrandom spec a509 -5170 v63 aLoss of species caused by widespread stressors, such as drought and fragmentation, is likely to be non-random depending on species abundance in the community. We experimentally reduced the number of rare and uncommon plant species while independently reducing only the abundance of dominant grass species in intact, native grassland. This allowed us to simulate a non-random pattern of species loss, based on species abundances, from communities shaped by natural ecological interactions and characterized by uneven species abundance distributions. Over two growing seasons, total above-ground net primary productivity (ANPP) declined with reductions in abundance of the dominant species but was unaffected by a threefold decline in richness of less common species. In contrast, productivity of the remaining rare and uncommon species decreased with declining richness, in part due to loss of complementary interactions among these species. However, increased production of the dominant grasses offset the negative effects of species loss. We conclude that the dominant species, as controllers of ecosystem function, can provide short-term resistance to reductions in ecosystem function when species loss is nonrandom. However, the concurrent loss of complementary interactions among rare and uncommon species, the most diverse component of communities, may contribute to additional species loss and portends erosion of ecosystem function in the long term.1 aSmith, M.D.1 aKnapp, Alan, K. uhttp://knz.lternet.edu/content/dominant-species-maintain-ecosystem-function-non-random-species-loss00579nas a2200121 4500008004100000245013500041210006900176260004300245300001100288490002100299100001600320856012100336 2002 eng d00aCauses and consequences of species invasion and loss: the role of dominant species and diversity in maintaining ecosystem function0 aCauses and consequences of species invasion and loss the role of aManhattan, KSbKansas State University a1 -1480 vPhD Dissertation1 aSmith, M.D. uhttp://knz.lternet.edu/content/causes-and-consequences-species-invasion-and-loss-role-dominant-species-and-diversity01540nas a2200229 4500008004100000245009000041210006900131300001500200490000800215520084900223100002001072700001401092700002001106700002401126700001601150700001901166700001701185700001701202700001501219700001901234856005701253 2002 eng d00aRainfall variability, carbon cycling and plant species diversity in a mesic grassland0 aRainfall variability carbon cycling and plant species diversity  a2202 -22050 v2983 a

Ecosystem responses to increased variability in rainfall, a prediction of general circulation models, were assessed in native grassland by reducing storm frequency and increasing rainfall quantity per storm during a 4-year experiment. More extreme rainfall patterns, without concurrent changes in total rainfall quantity, increased temporal variability in soil moisture and plant species diversity. However, carbon cycling processes such as soil CO2 flux, CO2 uptake by the dominant grasses, and aboveground net primary productivity (ANPP) were reduced, and ANPP was more responsive to soil moisture variability than to mean soil water content. Our results show that projected increases in rainfall variability can rapidly alter key carbon cycling processes and plant community composition, independent of changes in total precipitation.

1 aKnapp, Alan, K.1 aFay, P.A.1 aBlair, John, M.1 aCollins, Scott., L.1 aSmith, M.D.1 aCarlisle, J.D.1 aHarper, C.W.1 aDanner, B.T.1 aLett, M.S.1 aMcCarron, J.K. uhttps://science.sciencemag.org/content/298/5601/220202599nas a2200193 4500008004100000245007900041210006900120300001500189490000700204520203100211653001502242653000902257653002202266100001702288700001902305700001602324700001702340856004802357 2001 eng d00aEffects of mycorrhizas on growth and demography of tallgrass prairie forbs0 aEffects of mycorrhizas on growth and demography of tallgrass pra a1452 -14570 v883 aThe effects of arbuscular mycorrhizal (AM) symbiosis on ramet and genet densities, vegetative growth rates, and flowering of three forb species were studied in native tallgrass prairie in northeastern Kansas. Mycorrhizal activity was experimentally suppressed for six growing seasons on replicate plots in an annually burned and an infrequently burned watershed with the fungicide benomyl. Benomyl reduced mycorrhizal root colonization to an average of 4.2%, approximately a two-thirds reduction relative to controls (13.7% colonization). Mycorrhizae influenced the population structure of these forbs. Although mycorrhizal suppression had no long-term effect on genet densities and no effect on ramet survivorship throughout the growing season, the number of ramets per individual was significantly increased such that ramet densities of all three species were approximately doubled in response to long-term mycorrhizal suppression. Effects of mycorrhizae on ramet growth and reproduction varied among species. Ramet growth rates, biomass, and flowering of Salvia azurea were greater in plots with active mycorrhizal symbiosis, whereas mycorrhizae reduced ramet growth rates and biomass of Artemesia ludoviciana. Aster sericeus ramet growth rates and biomass were unaffected by the fungicide applications, but its flowering was reduced.The pattern of responses of these three species to mycorrhizae differed considerably between the two sites of contrasting fire regime, indicating that the interaction of fire-induced shifts in resource availability and mycorrhizal symbiosis together modulates plant responses and the intensity and patterns of interspecific competition between and among tallgrass prairie grass and forb species. Further, the results indicate that effects of mycorrhizae on community structure are a result of interspecific differences in the balance between direct positive effects of the symbiosis on host plant performance and indirect negative effects mediated through altered competitive interactions.10ademography10aforb10atallgrass prairie1 aWilson, G.T.1 aHartnett, D.C.1 aSmith, M.D.1 aKobbeman, K. uhttp://www.ncbi.nlm.nih.gov/pubmed/2166967804557nas a2200265 4500008004100000245009100041210006900132260005100201300001100252520369800263653001703961653001903978653000903997653001504006653002004021653001204041100001604053700001604069700001604085700002404101700002004125700001504145700001504160856011604175 2001 eng d00aInteractions between fire and invasive plants in temperate grasslands of North America0 aInteractions between fire and invasive plants in temperate grass aTallahassee, FLbTall Timbers Research Station a40 -653 aA substantial number of invasive grasses, forbs and woody plants have invaded temperate grasslands in North America. Among the invading species are winter annuals, biennials, cool-season perennials, warm-season perennials, vines, shrubs, and trees. Many of these species have been deliberately introduced and widely planted; some are still used for range improvement, pastures, lawns, and as ornamentals, though many are listed as state or federal noxious weeds. Others have been greatly facilitated by widespread land disturbance. Historically, fire has been a major selective force in the evolution of temperate grasslands. Further, prescribed fire is commonly used as a method of ecological management for native grassland communities as well as in conjunction with restoration efforts. Within this context, it is important to understand how invasive species will interact with natural and prescribed fire regimes. In this paper, we consider what is known about how exotic species that invade temperate grasslands relate to fire. The primary issues addressed for each species are (1) Does fire appear to enhance colonization? (2) To what degree does fire affect the survival of plants? (3) Are plants that are burned able to regrow following fire and, if so, how rapidly can they recover? (4) How important is competition with native species to the response to fire? and (5) What effect does an invasive species have on the characteristics of the fire regime? For many species, results are preliminary, incomplete, or inconsistent among studies. For this reason, many of the conclusions drawn for individual species must be considered preliminary. Based on analyses of individual species, a conceptual framework is presented for considering how invasive plants may interact with fire when they invade an ecosystem. The major categories of influences are the native community, the fire regime, growth conditions for both invasive and native species, and influences that disturbances, human impacts, and landscape characteristics have had in the past and will have in the future. The examples considered in this paper provide support for a few, tentative generalizations. First, among our current worst invaders of temperate grasslands, adaptation to fire is quite variable. Some species are not well adapted to burning and can be easily eliminated; other species are better adapted but can still be eliminated if fire occurs during periods of particular vulnerability and/or at high frequency. There is a set of species that is extremely well adapted to fire and will not be eliminated through burning alone. Second, competitive interactions with native species play a crucial role in the success of nonnative invaders. In cases where differential burn responses between invasive and native species can be exploited, and adequate populations of native dominant species are present, fire can sometimes tip the competitive balance away from invasives. Third, there are a few invasive species that have exceptional attributes and for which there are no easy solutions. The ability of cheatgrass (Bromus tectorum) to enhance fire, the ability of Chinese tallow (Triadica sebifera) to suppress fire, and the ability of leafy spurge (Euphorbia esula) to resprout from repeated injury make the sespecies exceptional threats to native diversity. Finally, the available information for many invasive species is very incomplete, particularly with regard to how fire affects competitive interactions with the native community. There is much more we need to know if we are to consistently predict how invasive species will respond to fire and how burning can best be used to manage for natural diversity10aalien plants10aexotic species10afire10aGrasslands10ainvasive plants10aprairie1 aGrace, J.B.1 aSmith, M.D.1 aGrace, S.L.1 aCollins, Scott., L.1 aStohlgren, T.J.1 aGalley, K.1 aWilson, T. uhttp://knz.lternet.edu/content/interactions-between-fire-and-invasive-plants-temperate-grasslands-north-america02509nas a2200193 4500008004100000245011700041210006900158300001300227490000800240520181000248653002302058653001402081653002002095653001902115653002302134100001602157700002002173856012202193 2001 eng d00aPhysiological and morphological traits of exotic, invasive exotic, and native plant species in tallgrass prairie0 aPhysiological and morphological traits of exotic invasive exotic a785 -7920 v1623 aWe compared 13 traits of invasive exotic, noninvasive exotic, and ecologically similar native species to determine if there are generalizable differences among these groups that relate to persistence and spread of exotic species in tallgrass prairie plant communities. When species were grouped as invasive (two species), noninvasive (five species), and native (six species), no differences were found for the suite of traits examined, likely because of the high variability within and between groups. However, when exotic species, regardless of invasiveness, were compared with the native species, specific leaf area was ca. 40% higher for the exotic species, a result that is consistent with that of other studies. This pattern was also observed for five of seven pairwise comparisons of exotic and native species with similar life history traits. In contrast, total end‐of‐season biomass was as much as three times higher for the native species in five of seven of the native‐exotic species pairs. For other traits, differences between exotic and native species were species‐specific and were generally more numerous for noninvasive than for invasive exotic species pair‐wise comparisons. Thus, contrary to predictions, exotic species capable of successfully invading tallgrass prairie did not differ considerably from native species in most traits related to resource utilization and carbon gain. Moreover, invasive exotic species, those capable of displacing native species and dominating a community, were not distinct for the observed traits from their native counterparts. These results indicate that other traits, such as the ability to respond to resource pulses or herbivory, may explain more effectively why certain invasive species are able to invade these communities aggressively.10abiomass allocation10agrassland10ainvasive plants10aphotosynthesis10aspecific leaf area1 aSmith, M.D.1 aKnapp, Alan, K. uhttp://knz.lternet.edu/content/physiological-and-morphological-traits-exotic-invasive-exotic-and-native-plant-species02871nas a2200133 4500008004100000245008700041210006900128300001100197490000700208520238000215100001602595700002002611856010602631 2001 eng d00aSize of the local species pool determines invasibility of a C4-dominated grassland0 aSize of the local species pool determines invasibility of a C4do a55 -610 v923 aThe size of the local species pool (i.e., species surrounding a community capable of dispersal into that community) and other dispersal limitations strongly influence native plant community composition. However, the role that the local species pool plays in determining the invasibility of communities by exotic plants remains to be evaluated. We hypothesized that the richness and abundance of exotic species would be greater in C4-dominated grassland communities if the local species pool included a larger proportion of exotic species. We also predicted that an increase in the exotic species pool would increase the invasibility of sites thought to be resistant to invasion (annually burned grassland). To test these hypotheses, study plots were established within two long-term (>20 yr) fire experiments at a tallgrass prairie preserve in NE Kansas (USA). Study plots were surrounded by either a small pool of exotic species (small species pool (SSP) plots; six species) or a larger exotic species pool (large species pool (LSP) plots; 18 species). We found that richness and absolute cover of exotic species was significantly (P<0.001) lower (∼70 and 90%, respectively) in annually burned compared to unburned plots, regardless of the size of the exotic species pool. As predicted, exotic species richness was higher (P<0.001) for LSP plots (3.9 per 250 m2) than for SSP plots (0.7 per 250 m2); however, absolute cover was unaffected by the size of the exotic species pool. In the absence of fire, plots with a LSP had four times as many exotic species than SSP plots. An increase in the local exotic species pool also increased the invasibility of annually burned grassland. Indeed, richness of exotic plant species in annually burned LSP plots did not differ from unburned plots with a SSP, indicating that a larger pool of exotic species countered the negative effects of fire. These findings have important implications for predicting how the invasion of plant communities may respond to human-induced global changes, such as habitat fragmentation. Community characteristics or factors such as frequent fires in grasslands may impart resistance to invasions by exotic species in large, intact ecosystems. However, when a large pool of exotic species is present, frequent fire may not be sufficient to limit the invasions of exotic plants in fragmented landscapes.1 aSmith, M.D.1 aKnapp, Alan, K. uhttp://knz.lternet.edu/content/size-local-species-pool-determines-invasibility-c4-dominated-grassland01447nas a2200145 4500008004100000245008200041210006900123300001300192490000800205520092200213653002301135100002001158700001601178856010701194 2001 eng d00aVariation among biomes in temporal dynamics of aboveground primary production0 aVariation among biomes in temporal dynamics of aboveground prima a481 -4840 v2913 aInterannual variability in aboveground net primary production (ANPP) was assessed with long-term (mean = 12 years) data from 11 Long Term Ecological Research sites across North America. The greatest interannual variability in ANPP occurred in grasslands and old fields, with forests the least variable. At a continental scale, ANPP was strongly correlated with annual precipitation. However, interannual variability in ANPP was not related to variability in precipitation. Instead, maximum variability in ANPP occurred in biomes where high potential growth rates of herbaceous vegetation were combined with moderate variability in precipitation. In the most dynamic biomes, ANPP responded more strongly to wet than to dry years. Recognition of the fourfold range in ANPP dynamics across biomes and of the factors that constrain this variability is critical for detecting the biotic impacts of global change phenomena.10aPrimary production1 aKnapp, Alan, K.1 aSmith, M.D. uhttp://knz.lternet.edu/content/variation-among-biomes-temporal-dynamics-aboveground-primary-production03159nas a2200217 4500008004100000245009700041210006900138300001300207490000700220520243800227653003302665653001202698653001102710653002202721653001402743653001302757100001602770700001902786700001702805856011902822 2000 eng d00aEffects of long-term fungicide application on microbial processes in tallgrass prairie soils0 aEffects of longterm fungicide application on microbial processes a935 -9460 v323 aSeveral studies investigating the role of arbuscular mycorrhizal (AM) fungi in plant communities have included manipulations of AM fungal symbiosis using the fungicide benomyl. The objectives of this study were to evaluate the potential non-target effects of benomyl on soil biota and nutrient cycling in tallgrass prairie and to determine how mycorrhizae may influence these belowground properties. To accomplish these objectives, soil samples were collected during the 1996–1997 growing seasons from long-term benomyl-treated plots established on tallgrass prairie (Manhattan, KS) in 1991, and the following measurements were made: total bacterial and fungal biomass; abundance of nematodes; microbial biomass carbon and nitrogen; substrate-induced respiration; and potentially mineralizable C and N. Long-term benomyl applications resulted in an 80% reduction in mycorrhizal root colonization. By reducing root colonization, benomyl applications resulted in significant decreases in total bacterial biomass and abundance of fungal-feeding and predatory nematodes (20, 12 and 33% reductions compared to control, respectively). Total microbial potential activity (i.e., substrate-induced respiration) increased by 10% with benomyl treatment, whereas the relative contribution of fungi to total microbial activity decreased significantly with benomyl applications. In addition, microbial biomass C increased from 1364 (± 51.2 SE) to 1485 (± 51.2 SE) with benomyl treatment, and total carbon increased significantly (∼8%) only in annually burned soils treated with benomyl. The magnitude of benomyl effects on soil components and processes were small (<33% change with benomyl) relative to effects on mycorrhizal root colonization (80% decrease with benomyl). These results indicate that rather than having large non-target effects, benomyl applications principally affect mycorrhizal root colonization, thereby indirectly influencing soil biota and nutrient availability. Results also indicate that mycorrhizal fungi play an important role in altering the availability and flow of carbon in prairie soil and may influence the composition and abundance of groups of some soil biota. Changes in soil organisms and nutrient availability associated with altered mycorrhizal symbiosis may influence aboveground plant species responses to mycorrhizal suppression, but further research is needed to understand these potential effects.10aArbuscular mycorrhizal fungi10aBenomyl10acarbon10aMicrobial biomass10aNematodes10anitrogen1 aSmith, M.D.1 aHartnett, D.C.1 aRice, C., W. uhttp://knz.lternet.edu/content/effects-long-term-fungicide-application-microbial-processes-tallgrass-prairie-soils02315nas a2200193 4500008004100000245010400041210006900145300001300214490000800227520163200235653002401867653001601891653001901907653001401926653001701940100001601957700002001973856012801993 1999 eng d00aExotic plant species in a C4-dominated grassland: Invasibility, disturbance and community structure0 aExotic plant species in a C4dominated grassland Invasibility dis a605 -6120 v1203 aWe used data from a 15-year experiment in a C4-dominated grassland to address the effects of community structure (i.e., plant species richness, dominance) and disturbance on invasibility, as measured by abundance and richness of exotic species. Our specific objectives were to assess the temporal and spatial patterns of exotic plant species in a native grassland in Kansas (USA) and to determine the factors that control exotic species abundance and richness (i.e., invasibility). Exotic species (90% C3 plants) comprised approximately 10% of the flora, and their turnover was relatively high (30%) over the 15-year period. We found that disturbances significantly affected the abundance and richness of exotic species. In particular, long-term annually burned watersheds had lower cover of exotic species than unburned watersheds, and fire reduced exotic species richness by 80–90%. Exotic and native species richness were positively correlated across sites subjected to different fire (r = 0.72) and grazing (r = 0.67) treatments, and the number of exotic species was lowest on sites with the highest productivity of C4 grasses (i.e., high dominance). These results provide strong evidence for the role of community structure, as affected by disturbance, in determining invasibility of this grassland. Moreover, a significant positive relationship between exotic and native species richness was observed within a disturbance regime (annually burned sites, r = 0.51; unburned sites, r = 0.59). Thus, invasibility of this C4-dominated grassland can also be directly related to community structure independent of disturbance.10acommunity structure10adisturbance10aexotic species10agrassland10aInvasibility1 aSmith, M.D.1 aKnapp, Alan, K. uhttp://knz.lternet.edu/content/exotic-plant-species-c4-dominated-grassland-invasibility-disturbance-and-community-structure02670nas a2200205 4500008004100000245010700041210006900148300001300217490000800230520194400238653003302182653001602215653001402231653002402245653002202269100001602291700001902307700001702326856012102343 1999 eng d00aInteracting influence of mycorrhizal symbiosis and competition on plant diversity in tallgrass prairie0 aInteracting influence of mycorrhizal symbiosis and competition o a574 -5820 v1213 aIn tallgrass prairie, plant species interactions regulated by their associated mycorrhizal fungi may be important forces that influence species coexistence and community structure; however, the mechanisms and magnitude of these interactions remain unknown. The objective of this study was to determine how interspecific competition, mycorrhizal symbiosis, and their interactions influence plant community structure. We conducted a factorial experiment, which incorporated manipulations of abundance of dominant competitors, Andropogon gerardii and Sorghastrum nutans, and suppression of mycorrhizal symbiosis using the fungicide benomyl under two fire regimes (annual and 4-year burn intervals). Removal of the two dominant C4 grass species altered the community structure, increased plant species richness, diversity, and evenness, and increased abundance of subdominant graminoid and forb species. Suppression of mycorrhizal fungi resulted in smaller shifts in community structure, although plant species richness and diversity increased. Responses of individual plant species were associated with their degree of mycorrhizal responsiveness: highly mycorrhizal responsive species decreased in abundance and less mycorrhizal responsive species increased in abundance. The combination of dominant-grass removal and mycorrhizal suppression treatments interacted to increase synergistically the abundance of several species, indicating that both processes influence species interactions and community organization in tallgrass prairie. These results provide evidence that mycorrhizal fungi affect plant communities indirectly by influencing the pattern and strength of plant competitive interactions. Burning strongly influenced the outcome of these interactions, which suggests that plant species diversity in tallgrass prairie is influenced by a complex array of interacting processes, including both competition and mycorrhizal symbiosis.10aArbuscular mycorrhizal fungi10aCompetition10adiversity10aSpecies coexistence10atallgrass prairie1 aSmith, M.D.1 aHartnett, D.C.1 aWilson, G.T. uhttp://knz.lternet.edu/content/interacting-influence-mycorrhizal-symbiosis-and-competition-plant-diversity-tallgrass00601nas a2200133 4500008004100000245012600041210006900167260004300236300001100279490001400290653002200304100001600326856012500342 1998 eng d00aThe role of mycorrhizae and dominant competitors in tallgrass prairie plant community structure and belowground processes0 arole of mycorrhizae and dominant competitors in tallgrass prairi aManhattan, KSbKansas State University a1 -1390 vMS Thesis10atallgrass prairie1 aSmith, M.D. uhttp://knz.lternet.edu/content/role-mycorrhizae-and-dominant-competitors-tallgrass-prairie-plant-community-structure-and