00541nas a2200157 4500008004100000022001400041245010800055210006900163300001400232490000800246100001700254700001500271700001700286700002300303856005700326 2024 eng d a0029-854900aCombined effects of fire and drought are not sufficient to slow shrub encroachment in tallgrass prairie0 aCombined effects of fire and drought are not sufficient to slow  a727 - 7420 v2041 aKeen, R., M.1 aBachle, S.1 aBartmess, M.1 aNippert, Jesse, B. uhttps://link.springer.com/10.1007/s00442-024-05526-x00507nas a2200145 4500008004100000245007600041210006900117300001400186490000800200100002400208700002300232700002100255700002800276856005700304 2024 eng d00aContrasting shrub and grass hydraulic responses to experimental drought0 aContrasting shrub and grass hydraulic responses to experimental  a931 - 9410 v2041 aO’Keefe, Kimberly1 aNippert, Jesse, B.1 aKeen, Rachel, M.1 aMcCulloh, Katherine, A. uhttps://link.springer.com/10.1007/s00442-024-05543-w00531nas a2200121 4500008004100000245016500041210006900206490000800275100001800283700002300301700001800324856006700342 2024 eng d00aEvaluating methods for measuring the leaf area index of encroaching shrubs in grasslands: From leaves to optical methods, 3-D scanning, and airborne observation0 aEvaluating methods for measuring the leaf area index of encroach0 v3491 aTooley, E., G1 aNippert, Jesse, B.1 aRatajczak, Z. uhttps://linkinghub.elsevier.com/retrieve/pii/S016819232400079000529nas a2200145 4500008004100000245009300041210007100134300001200205490000800217100001700225700002100242700002100263700002300284856007600307 2024 eng d00aSave or spend? Diverging water‐use strategies of grasses and encroaching clonal shrubs0 aSave or spend Diverging water‐use strategies of grasses and encr a870-8850 v1121 aKeen, R., M.1 aHelliker, B., R.1 aMcCulloh, K., A.1 aNippert, Jesse, B. uhttps://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2745.1427600589nas a2200181 4500008004100000245008200041210006900123300001100192490000800203100001500211700001900226700001800245700001100263700001500274700001900289700002300308856007600331 2024 eng d00aUnexpected hydrologic response to ecosystem state change in tallgrass prairie0 aUnexpected hydrologic response to ecosystem state change in tall a1319370 v6431 aKeen, R.M.1 aSadayappan, K.1 aJarecke, K.M.1 aLi, L.1 aKirk, M.F.1 aSullivan, P.L.1 aNippert, Jesse, B. uhttps://www.sciencedirect.com/science/article/abs/pii/S002216942401333700606nas a2200181 4500008004100000245009400041210006900135300001200204490000700216100002100223700002300244700001900267700001800286700001900304700001800323700001800341856006500359 2023 eng d00aImpacts of riparian and non-riparian woody encroachment on tallgrass prairie ecohydrology0 aImpacts of riparian and nonriparian woody encroachment on tallgr a290-3010 v261 aKeen, Rachel, M.1 aNippert, Jesse, B.1 aSullivan, P.L.1 aRatajczak, Z.1 aRitchey, Brynn1 aO’Keefe, K.1 aDodds, W., K. uhttps://link.springer.com/article/10.1007/s10021-022-00756-700497nas a2200145 4500008004100000245009000041210006900131100002300200700001900223700001800242700001700260700001700277700001700294856004000311 2023 eng d00aUsing root and soil traits to forecast woody encroachment dynamics in mesic grassland0 aUsing root and soil traits to forecast woody encroachment dynami1 aNippert, Jesse, B.1 aMcCulloh, Kate1 aWilcox, Kevin1 aO'Keefe, Kim1 aKeen, Rachel1 aChen, Anping uhttps://www.osti.gov/biblio/224806102538nas a2200193 4500008004100000020001800041245010700059210006900166250000600235260000800241300000700249520183800256100002302094700001502117700001802132700001602150700001902166856015902185 2022 eng d a978036747833900aClimate change in grassland ecosystems: current impacts and potential actions for a sustainable future0 aClimate change in grassland ecosystems current impacts and poten a1 bCRC a363 a

Grasslands are a widespread and globally important biome providing key ecosystem services, including carbon storage, regulation of the water cycle and diverse assemblages of plant and animal species. Grasslands also provide many important benefits to humans, such as food and forage for livestock. Climate changes manifest as temperature fluctuations, increased intensity of drought and flood cycles and increased atmospheric CO2 concentrations. These changes are impacting species growth responses, plant composition and other key grassland processes. In addition to the direct consequences of climate change, secondary (or indirect) impacts of climate change threaten grassland ecosystems. These include changes in land-use and land-cover, agricultural conversion, woody encroachment, invasive species and atmospheric nitrogen deposition. In this chapter, we discuss the direct and indirect impacts of climate change on grasslands generally, while using case studies from specific global grassland types to illustrate key threats and climate change impacts. We specifically provide examples of how direct and indirect climate changes interact, increasing the vulnerability of grasslands. In the final section of this chapter, we outline a climate action plan for grassland ecosystems that includes efforts focused at multiple scales, including the individual, community and global levels. These climate actions can be used to influence policy, reduce the rate of climate change, conserve and restore grasslands and, most importantly, need to begin immediately. Collectively, we explain the general ecological processes in grasslands, illustrate the consequences of climate change on this ecosystem and identify potential solutions to maintain the viability and persistence of grassland ecosystems for the foreseeable future.

1 aNippert, Jesse, B.1 aKeen, R.M.1 aBachle, Seton1 aWedel, E.R.1 aGroskinsky, B. uhttps://www.taylorfrancis.com/chapters/edit/10.1201/9781003048701-4/climate-change-grassland-ecosystems-jesse-nippert-seton-bachle-rachel-keen-emily-wedel00577nas a2200145 4500008004100000245013100041210006900172300001600241490000700257100001900264700002300283700001900306700001500325856009100340 2022 eng d00aIntra-canopy leaf trait variation facilitates high leaf area index and compensatory growth in a clonal woody-encroaching shrub0 aIntracanopy leaf trait variation facilitates high leaf area inde a2186–22020 v421 aTooley, E., G.1 aNippert, Jesse, B.1 aBachle, Seton.1 aKeen, R.M. uhttps://academic.oup.com/treephys/advance-article/doi/10.1093/treephys/tpac078/664798400640nas a2200181 4500008004100000245009900041210006900140300001600209490000700225100002600232700002300258700002000281700002200301700002300323700002600346700002600372856006000398 2022 eng d00aKernel weight contribution to yield genetic gain of maize: a global review and US case studies0 aKernel weight contribution to yield genetic gain of maize a glob a3597 - 36090 v731 aFernández, Javier, A1 aMessina, Carlos, D1 aSalinas, Andrea1 aPrasad, P, V Vara1 aNippert, Jesse, B.1 aCiampitti, Ignacio, A1 aDreisigacker, Susanne uhttps://academic.oup.com/jxb/article/73/11/3597/654790100874nas a2200277 4500008004100000245012500041210006900166300001000235490000700245100002000252700002100272700002200293700002000315700001400335700002300349700001600372700001800388700001500406700001600421700001600437700001900453700001700472700001700489700001600506856007400522 2022 eng d00aN and P constrain C in ecosystems under climate change: role of nutrient redistribution, accumulation, and stoichiometry0 aN and P constrain C in ecosystems under climate change role of n ae26840 v321 aRastetter, E.B.1 aKwiakowski, B.L.1 aKicklighter, D.W.1 aPlotkin, Barker1 aGenet, H.1 aNippert, Jesse, B.1 aO'Keefe, K.1 aPerakis, S.R.1 aPorder, S.1 aRoley, S.S.1 aReuss, R.W.1 aThompson, J.R.1 aWieder, W.R.1 aWilcox, K.R.1 aYanai, R.D. uhttps://esajournals.onlinelibrary.wiley.com/doi/full/10.1002/eap.268400742nas a2200217 4500008004100000245012800041210006900169300001100238490000800249100001900257700002300276700001900299700001700318700001800335700002400353700002100377700002300398700002700421700002100448856005500469 2022 eng d00aPoor relationships between NEON Airborne Observation Platform data and field‐based vegetation traits at a mesic grassland0 aPoor relationships between NEON Airborne Observation Platform da ae035900 v1031 aPau, Stephanie1 aNippert, Jesse, B.1 aSlapikas, Ryan1 aGriffith, D.1 aBachle, Seton1 aHelliker, Brent, R.1 aO’Connor, R.C.1 aRiley, William, J.1 aStill, Christopher, J.1 aZaricor, Marissa uhttps://onlinelibrary.wiley.com/toc/19399170/103/200595nas a2200157 4500008004100000245011800041210006900159300001100228490000800239100002600247700002300273700002300296700002400319700002700343856006700370 2022 eng d00aPost-silking 15N labelling reveals an enhanced nitrogen allocation to leaves in modern maize (Zea mays) genotypes0 aPostsilking 15N labelling reveals an enhanced nitrogen allocatio a1535770 v2681 aFernandez, Javier, A.1 aNippert, Jesse, B.1 aPrasad, P.V., Vara1 aMessina, Carlos, D.1 aCiampitti, Ignacio, A. uhttps://linkinghub.elsevier.com/retrieve/pii/S017616172100216901990nas a2200205 4500008004100000245009500041210006900136300001600205490000800221520135500229100001801584700001701602700001801619700001801637700001801655700001801673700001701691700002301708856005301731 2022 eng d00aReintroducing bison results in long-running and resilient increases in grassland diversity0 aReintroducing bison results in longrunning and resilient increas ae22104331190 v1193 a

The widespread extirpation of megafauna may have destabilized ecosystems and altered biodiversity globally. Most megafauna extinctions occurred before the modern record, leaving it unclear how their loss impacts current biodiversity. We report the long-term effects of reintroducing plains bison (Bison bison) in a tallgrass prairie versus two land uses that commonly occur in many North American grasslands: 1) no grazing and 2) intensive growing-season grazing by domesticated cattle (Bos taurus). Compared to ungrazed areas, reintroducing bison increased native plant species richness by 103% at local scales (10 m2) and 86% at the catchment scale. Gains in richness continued for 29 y and were resilient to the most extreme drought in four decades. These gains are now among the largest recorded increases in species richness due to grazing in grasslands globally. Grazing by domestic cattle also increased native plant species richness, but by less than half as much as bison. This study indicates that some ecosystems maintain a latent potential for increased native plant species richness following the reintroduction of native herbivores, which was unmatched by domesticated grazers. Native-grazer gains in richness were resilient to an extreme drought, a pressure likely to become more common under future global environmental change.

1 aRatajczak, Z.1 aCollins, S.L1 aBlair, J., M.1 aKoerner, S.E.1 aLouthan, A.M.1 aSmith, M., D.1 aTaylor, J.H.1 aNippert, Jesse, B. uhttps://www.pnas.org/doi/10.1073/pnas.221043311900553nas a2200157 4500008004100000245011300041210006900154300001400223490000700237100002200244700001800266700001700284700001700301700002300318856005400341 2022 eng d00aRoot traits reveal safety and efficiency differences in grasses and shrubs exposed to different fire regimes0 aRoot traits reveal safety and efficiency differences in grasses  a368 - 3790 v361 aO'Keefe, Kimberly1 aBachle, Seton1 aKeen, Rachel1 aTooley, Greg1 aNippert, Jesse, B. uhttps://onlinelibrary.wiley.com/toc/13652435/36/200470nas a2200121 4500008004100000245008600041210006900127260004300196490001400239100001800253700002300271856005400294 2022 eng d00aThe unique canopy structure, leaf morphology, and physiology of Cornus drummondii0 aunique canopy structure leaf morphology and physiology of Cornus aManhattan, KSbKansas State University0 vMS Thesis1 aTooley, E., G1 aNippert, Jesse, B. uhttps://krex.k-state.edu/dspace/handle/2097/4216200480nas a2200121 4500008004100000245008900041210006900130260004300199490002100242100001800263700002300281856005400304 2021 eng d00aAnatomical constraints on grass physiological responses depend on water availability0 aAnatomical constraints on grass physiological responses depend o aManhattan, KSbKansas State University0 vPhD Dissertation1 aBachle, Seton1 aNippert, Jesse, B. uhttps://krex.k-state.edu/dspace/handle/2097/4135400616nas a2200169 4500008004100000245012100041210006900162300001200231490000700243100001600250700001800266700002300284700001700307700002100324700002200345856007900367 2021 eng d00aSpatio-temporal differences in leaf physiology are associated with fire, not drought, in a clonally integrated shrub0 aSpatiotemporal differences in leaf physiology are associated wit aplab0370 v131 aWedel, E.R.1 aO’Keefe, K.1 aNippert, Jesse, B.1 aHoch, Braden1 aO’Connor, R.C.1 aMitchell, Patrick uhttps://academic.oup.com/aobpla/article/doi/10.1093/aobpla/plab037/629532500463nas a2200121 4500008004100000245007900041210006900120260004300189490001400232100001800246700002300264856005400287 2021 eng d00aA study of grass structure and function in response to drought and grazing0 astudy of grass structure and function in response to drought and aManhattan, KSbKansas State University0 vMS Thesis1 aZaricor, M.L.1 aNippert, Jesse, B. uhttps://krex.k-state.edu/dspace/handle/2097/4151402430nas a2200157 4500008004100000245012000041210007100161300001800232490000800250520184800258100002202106700002002128700002802148700002302176856007302199 2020 eng d00aBridging the flux gap: Sap flow measurements reveal species‐specific patterns of water use in a tallgrass prairie0 aBridging the flux gap Sap flow measurements reveal species‐speci ae2019JG0054460 v1253 a

Predicting the hydrological consequences following changes in grassland vegetation type (i.e., woody encroachment) requires an understanding of water flux dynamics at high spatiotemporal resolution for predominant species within grassland communities. However, grassland fluxes are typically measured at the leaf or landscape scale, which inhibits our ability to predict how individual species contribute to changing ecosystem fluxes. We used external heat balance sap flow sensors and a hierarchical Bayesian state‐space modeling approach to bridge this “flux gap” and estimate continuous species‐level water flux in common tallgrass prairie species. Specifically, we asked the following: (1) How do diurnal and nocturnal water fluxes differ among woody and herbaceous plants? (2) How sensitive are woody and herbaceous species to environmental drivers of diurnal and nocturnal water flux? We highlight three results: (1) Cornus drummondii, the primary woody encroacher in this grassland, exhibited the greatest canopy‐level water loss; (2) nocturnal transpiration was a large component of the water lost in this ecosystem and was driven primarily by C4 grasses and C. drummondii; and (3) the sensitivity of canopy transpiration to environmental drivers varies among plant functional types and throughout a 24‐hr period. Our data reveal important insights regarding the water use strategies of woody versus herbaceous species in tallgrass prairies and about the potential hydrological consequences of ongoing woody encroachment. We suggest that the high, static flux rates observed in woody species will likely deplete deep water stores over time, potentially creating hydrological deficits in grasslands experiencing woody encroachment and concomitantly increasing the vulnerability of these ecosystems to drought.

1 aO'Keefe, Kimberly1 aBell, David, M.1 aMcCulloh, Katherine, A.1 aNippert, Jesse, B. uhttps://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2019JG00544602923nas a2200145 4500008004100000245009500041210006900136300001100205490000800216520241900224100002102643700001702664700002302681856007302704 2020 eng d00aBrowsing and fire decreases dominance of a resprouting shrub in woody encroached grassland0 aBrowsing and fire decreases dominance of a resprouting shrub in  ae029350 v1013 a

North American grasslands have experienced increased relative abundance of shrubs and trees over the last 150 years. Alterations in herbivore composition, abundance and grazing pressure along with changes in fire frequency are drivers that can regulate the transition from grassland to shrubland or woodland (a process known as woody encroachment). Historically, North American grasslands had a suite of large herbivores that grazed and/or browsed (i.e. bison, elk, pronghorn, deer), as well as frequent and intense fires. In the tallgrass prairie, many large native ungulates were extirpated by the 1860’s corresponding with increased homesteading (which led to decreased fire frequencies and intensities). Changes in the frequency and intensity of these two drivers (browsing and fire) has coincided with woody encroachment in tallgrass prairie. Within tallgrass prairie, woody encroachment can be categorized in to two groups: non‐resprouting species that can be killed with fire, and resprouting species that cannot be killed with fire. Resprouting species require additional active management strategies to decrease abundance and eventually be removed from the ecosystem. In this study we investigated plant cover, ramet density and physiological effects of continuous simulated browsing and prescribed fire on Cornus drummondii C.A. Mey, a resprouting clonal native shrub species. Browsing reduced C. drummondii canopy cover and increased grass cover. We also observed decreased ramet density that allowed for more infilling of grasses. Photosynthetic rates between browsed and unbrowsed control shrubs did not increase in 2015 or 2016. In 2017, photosynthetic rates for browsed shrubs were higher in the unburned site than the unbrowsed control shrubs at the end of the growing season. Additionally, after the prescribed fire, browsed shrubs had ~ 90% decreased cover, ~50% reduced ramet density, and grass cover increased by ~ 80%. In the roots of browsed shrubs after the prescribed fire, non‐structural carbohydrates (NSC) experienced a 2‐fold reduction in glucose and a 3‐fold reduction in both sucrose and starch. The combined effects of browsing and fire show strong potential as a successful management tool to decrease the abundance of clonal‐resprouting woody plants in mesic grasslands and illustrate the potential significance of browsers as a key driver in this ecosystem.

1 aO’Connor, R.C.1 aTaylor, J.H.1 aNippert, Jesse, B. uhttps://esajournals.onlinelibrary.wiley.com/doi/abs/10.1002/ecy.293500475nas a2200121 4500008004100000245008100041210006900122260004500191490002100236100001900257700002300276856005400299 2019 eng d00aDrivers, mechanisms, and thresholds of wood encroachment in mesic grasslands0 aDrivers mechanisms and thresholds of wood encroachment in mesic  aManhattan, KS. bKansas State University0 vPhD Dissertation1 aO'Connor, Rory1 aNippert, Jesse, B. uhttps://krex.k-state.edu/dspace/handle/2097/4002102371nas a2200193 4500008004100000245009500041210006900136300001100205490001200216520173500228100002101963700002001984700002702004700001902031700001802050700001902068700002302087856006702110 2019 eng d00aEvaluating a Lagrangian inverse model for inferring isotope CO2 exchange in plant canopies0 aEvaluating a Lagrangian inverse model for inferring isotope CO2  a1076510 v276-2773 a

Multi-layer Lagrangian models could be useful techniques for studying stable isotope exchange within and just above plant canopies. The main objective of this study was to evaluate the use of an analytical Lagrangian analysis (localized near-field theory, LNF), to study 13CO2 and C18OO isotope exchange in different plant canopies by comparing the LNF estimates with those provided by the eddy covariance (EC) technique and the isotope flux ratio method (IFR). Mixing ratios of stable isotopes of CO2 were measured within and above a temperate deciduous forest, tallgrass prairie and corn field using a multi-port sampling system and the tunable diode laser spectroscopy technique. Wind velocity data and the net CO2 ecosystem exchange (NEE) were measured above the plant canopies using an EC system. The wind velocity data and CO2 stable isotope mixing ratios were combined with the LNF theory to infer NEE and source/sinks of isotopes inside canopies. The LNF NEE estimates were likely affected by the flux decoupling in the forest canopy, resulting in a low correlation (R2 ranging from 0.03 to 0.35) between LNF and EC NEE estimates. On the other hand, LNF NEE estimates for corn and grassland canopies showed better correlation with EC NEE estimates (R2 ranging from 0.58 to 0.85), suggesting better coupling between in and above canopy air flows. Although, both LNF and IFR estimates showed large variability, our results show that the LNF approach reduced the uncertainties of the isotope compositions of NEE when compared to the IFR approach. These results suggest that LNF is a useful tool to study CO2 isotope exchange within short canopies where flux measurements are more challenging than inside tall canopies.

1 aSantos, Marshall1 aSantos, Eduardo1 aWagner-Riddle, Claudia1 aBrown, Shannon1 aStropes, Kyle1 aStaebler, Ralf1 aNippert, Jesse, B. uhttps://linkinghub.elsevier.com/retrieve/pii/S016819231930259X02414nas a2200205 4500008004100000245011200041210006900153300001100222490000700233520174800240100001701988700002302005700001902028700002102047700002302068700001702091700001402108700001602122856007002138 2018 eng d00aDeveloping a conceptual framework of landscape and hydrology on tallgrass prairie: A critical zone approach0 aDeveloping a conceptual framework of landscape and hydrology on  a1 - 110 v173 a

Agricultural intensification and urbanization have greatly reduced the extent of tallgrass prairie across North America. To evaluate the impact of these changes, a reference ecosystem of unperturbed prairie is required. The Konza Prairie Biological Station in northeastern Kansas is a long-term research site at which a critical zone approach has been implemented. Integration of climatic, ecologic, and hydropedologic research to facilitate a comprehensive understanding of the complex environment provides the basis for predicting future aquifer and landscape evolution. We present a conceptual framework of the hydrology underpinning the area that integrates the extensive current and past research and provides a synthesis of the literature to date. The key factors in the hydrologic behavior of Konza Prairie are climate, ecology, vadose zone characteristics and management, and groundwater and bedrock. Significant interactions among these factors include bedrock dissolution driven by cool-season precipitation and hence a climatic control on the rate of karstification. Soil moisture dynamics are influenced at various timescales due to the short- and long-term effects of prescribed burning on vegetation and on soil physical characteristics. The frequency of burning regimes strongly influences the expansion of woody species in competition with native tallgrasses, with consequent effects on C and N dynamics within the vadose zone. Knowledge gaps exist pertaining to the future of Konza Prairie (a model for US tallgrass prairie)—whether continued karstification will lead to increasingly flashy and dynamic hydrology and whether compositional changes in the vegetation will affect long-term changes in water balances.

1 aVero, S., E.1 aMacpherson, G., L.1 aSullivan, P.L.1 aBrookfield, A.E.1 aNippert, Jesse, B.1 aKirk, M., F.1 aDatta, S.1 aKempton, P. uhttps://dl.sciencesocieties.org/publications/vzj/pdfs/17/1/17006902767nas a2200145 4500008004100000245005900041210005900100300001400159490000700173520230700180100001602487700002302503700001502526856008002541 2018 eng d00aDrivers of nocturnal water flux in a tallgrass prairie0 aDrivers of nocturnal water flux in a tallgrass prairie a1155-11670 v323 a

Nocturnal transpiration can impact water balance from the local community to earth‐atmosphere fluxes. However, the dynamics and drivers of nocturnal transpiration among coexisting plant functional groups in herbaceous ecosystems are unknown.
Here, we addressed the following questions: (1) How do nocturnal (Enight) and diurnal (Eday) transpiration vary among coexisting grasses, forbs, and shrubs in a tallgrass prairie? (2) What environmental variables drive Enight and do these differ from the drivers of Eday? (3) Is Enight associated with daytime physiological processes?
We measured diurnal and nocturnal leaf gas exchange on perennial grass, forb and woody species in a North American tallgrass prairie. Measurements were made periodically across two growing seasons (May–August 2014–2015) on three C4 grasses (Andropogon gerardii, Sorghastrum nutans and Panicum virgatum), two C3 forbs (Vernonia baldwinii and Solidago canadensis), one C3 sub‐shrub (Amorpha canescens) and two C3 shrubs (Cornus drummondii and Rhus glabra).
By extending our study to multiple functional groups, we were able to make several key observations: (1) Enight was variable among co‐occurring plant functional groups, with the highest rates occurring in C4 grasses, (2) Enight and Eday exhibited different responses to vapour pressure deficit and other environmental drivers, and (3) rates of Enight were strongly related to predawn leaf water potential for grasses and woody species, and were likely modulated by small‐scale changes in soil moisture availability.
Our results provide novel insight into an often‐overlooked portion of ecosystem water balance. Considering the high rates of Enight observed in C4 grasses, as well as the widespread global occurrence of C4 grasses, nocturnal water loss might constitute a greater proportion of global evapotranspiration than previously estimated. Additionally, future predictions of nocturnal water loss may be complicated by stomatal behaviour that differs between the day and at night. Finally, these data suggest a water‐use strategy by C4 grasses wherein the high rates of Enight occurring during wet periods may confer a competitive advantage to maximize resource consumption during periods of greater availability.

1 aO'Keefe, K.1 aNippert, Jesse, B.1 aSala, Anna uhttps://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/1365-2435.1307202138nas a2200121 4500008004100000245010800041210006900149520166700218100001901885700001901904700002301923856007001946 2018 eng d00aIntraspecific trait variability in Andropogon gerardii, a dominant grass species in the US Great Plains0 aIntraspecific trait variability in Andropogon gerardii a dominan3 a

The climatic conditions in the North American Great Plains are highly variable, characteristic of an inter-continental climate. Antecedent climate history has impacted the flora of Great Plains grasslands, resulting in high species richness as well as dominance by only a few grass species, such as Andropogon gerardii. While the productivity of A. gerardii is well described, the individual physiological, and morphological characteristics that confer species dominance over wide spatial gradients are not clearly understood. We performed a literature search to assess intra-specific trait variability of A. gerardii from as many locations as possible. Ultimately, only 13 locations in the Great Plains have reported common plant functional traits (PFTs) for this species. To best represent site-specific climate conditions, plant functional trait data (8 PFTs) were collected from literature reporting ambient growing conditions, and excluded experimental manipulations. For most PFTs, we found insufficient data to fully quantify the range of variation across the geographical extent of A. gerardii dominance. This is surprising given that we focused on the most abundant grass in one of the most well-studied regions globally. Furthermore, trait data collected from our literature search showed a high degree of variability, but no strong relationships were observed between mean trait values and climate predictors. Our review of the literature on A. gerardii suggests a role for trait variability as a mechanism enabling the dominance of this species across large regions such as the Great Plains of North America.

1 aBachle, Seton.1 aGriffith, D.M.1 aNippert, Jesse, B. uhttps://www.frontiersin.org/articles/10.3389/fevo.2018.00217/full02033nas a2200133 4500008004100000245007400041210006900115300001200184490000700196520158700203100001901790700002301809856006701832 2018 eng d00aPhysiological and anatomical trait variability of dominant C4 grasses0 aPhysiological and anatomical trait variability of dominant C4 gr a14 - 200 v933 a

Climate variability is a key driver of physiological responses in common grass species in grasslands of North America. Differences in microanatomical traits among coexisting species may influence physiological responses to climate variability over large geographic scales. The goal of this research was to determine leaf-level physiological and microanatomical trait variability among four dominant C4 grass species across a natural precipitation gradient. Physiological traits were observed to vary significantly across the gradient with greater variability than microanatomical traits. Microanatomical traits were shown to predict physiological responses in A. gerardii and P. virgatum, but the nature of the relationships varied between species. These results illustrate that microanatomical and physiological traits vary across a precipitation gradient, there are clear linkages between microanatomy and physiology in grass species, and this evidence underscores the need for further investigation using phylogenetically diverse assemblages.

 

1 aBachle, Seton.1 aNippert, Jesse, B. uhttps://linkinghub.elsevier.com/retrieve/pii/S1146609X1730458702217nas a2200169 4500008004100000245012400041210006900165300001600234490000800250520162300258100001701881700002001898700001501918700001801933700002301951856007301974 2017 eng d00aAssessing the roles of fire frequency and precipitation in determining woody plant expansion in central U.S. grasslands0 aAssessing the roles of fire frequency and precipitation in deter a2683–26980 v1223 a

Woody plant expansion into grasslands and savannas is occurring and accelerating worldwide and often impacts ecosystem processes. Understanding and predicting the environmental and ecological impacts of encroachment has led to a variety of methodologies for assessing its onset, transition, and stability, generally relying on dynamical systems approaches. Here we continue this general line of investigation to facilitate the understanding of the roles of precipitation frequency and intensity and fire frequency on the conversion of grasslands to woody-dominated systems focusing on the central United States. A low-dimensional model with stochastic precipitation and fire disturbance is introduced to examine the complex interactions between precipitation and fire as mechanisms that may suppress or facilitate increases in woody cover. By using Lyapunov exponents, we are able to ascertain the relative control exerted on woody encroachment through these mechanisms. Our results indicate that precipitation frequency is a more important control on woody encroachment than the intensity of individual precipitation events. Fire, however, exerts a much more dominant impact on the limitation of encroachment over the range of precipitation variability considered here. These results indicate that fire management may be an effective strategy to slow the onset of woody species into grasslands. While climate change might predict a reduced potential for woody encroachment in the near future, these results indicate a reduction in woody fraction may be unlikely when considering anthropogenic fire suppression.

1 aBrunsell, N.1 avan Vleck, E.S.1 aNosshi, M.1 aRatajczak, Z.1 aNippert, Jesse, B. uhttps://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2017JG00404602066nas a2200205 4500008004100000245009100041210006900132260001600201300001400217490000800231520142400239653001901663653001101682653002201693653001801715653002001733100001801753700002301771856006601794 2017 eng d00aAn assessment of diurnal water uptake in a mesic prairie: evidence for hydraulic lift?0 aassessment of diurnal water uptake in a mesic prairie evidence f cFeb-02-2017 a963–9750 v1833 aHydraulic lift, the passive movement of water through plant roots from wet to dry soil, is an important ecohydrological process in a wide range of water-limited ecosystems. This phenomenon may also alter plant functioning, growth, and survival in mesic grasslands, where soil moisture is spatially and temporally variable. Here, we monitored diurnal changes in the isotopic signature of soil and plant xylem water to assess (1) whether hydraulic lift occurs in woody and herbaceous tallgrass prairie species (Rhus glabra, Amorpha canescens, Vernonia baldwinii, and Andropogon gerardii), (2) if nocturnal transpiration or grazing by large ungulates limits hydraulic lift, and (3) if a dominant grass, A. gerardii, utilizes water lifted by other tallgrass prairie species. Broadly, the results shown here suggest that hydraulic lift does not appear to be widespread or common in this system, but isolated instances suggest that this process does occur within tallgrass prairie. The isolated instance of hydraulic lift did not vary by grazing treatment, nor did they result in facilitation for neighboring grasses. We suggest that the topographic complexity of this tallgrass prairie and the high rates of nocturnal transpiration observed in this study likely limit the frequency and occurrence of hydraulic lift. These results suggest that hydraulic lift can be a patchy process, particularly in heterogeneous landscapes.10aHydraulic lift10aStable10atallgrass prairie10aTranspiration10aWater potential1 aO’Keefe, K.1 aNippert, Jesse, B. uhttps://link.springer.com/article/10.1007%2Fs00442-017-3827-203195nas a2200181 4500008004100000245008100041210006900122300001200191490000800203520260500211100001802816700002202834700002302856700002402879700001702903700001302920856008002933 2017 eng d00aChanges in spatial variance during a grassland to shrubland state transition0 aChanges in spatial variance during a grassland to shrubland stat a750-7600 v1053 a
  1. State transitions are changes in ecosystem structure and self-reinforcing feedbacks that are initiated when an exogenous driver variable crosses a threshold. Reversing state transitions is difficult and costly. While some state transitions are relatively rapid, many take years to decades. Outside of theoretical models, very little is known about slower state transitions and how they unfold in time and space.
  2. We quantified changes in spatial variance as a mesic grassland ecosystem shifts to a shrub-dominated state, using long-term experiments and simulations that maintain grasslands with annual fires or initiate a state transition to shrub dominance by decreasing fire frequency.
  3. In the experiments, the susceptibility to state transitions varied substantially in space. In the less frequent fire treatment, some plots became shrub-dominated around year 20 and grass extirpations began in year 25, but a third of the plots were still grass-dominated in year 37. Variable rates of state transition resulted in increasing spatial variance of grass cover over time, whereas shrub cover variance decreased. In the annually burned treatment, grasses remained dominant and the spatial variance of grass cover declined.
  4. In a separate experiment, less frequent fires were maintained for 23 years and then switched to annual fires. The switch to annual fires occurred shortly after grass variance started to increase and a majority of these plots quickly returned to a grass dominated state.
  5. In simulations, spatial variance remained low and average grass cover was high under frequent fires. If fire frequency decreased below a threshold, the ecosystem transitioned to shrubland, with a transient increase in the spatial variance of grass cover during the transition between states.
  6. Synthesis. Spatial variability in the rate and susceptibility to state transitions is indicative of a system with a patchy spatial structure, high spatial heterogeneity and low connectivity between patches. Increases in spatial variance can serve as an indication that some patches have begun a state transition and that management interventions are needed to avoid widespread transitions. This is one of the first empirical examples where altering management after an increase in spatial variance prevented state transitions.

 

1 aRatajczak, Z.1 aD’Odorico, P.D.1 aNippert, Jesse, B.1 aCollins, Scott., L.1 aBrunsell, N.1 aRavi, S. uhttps://besjournals.onlinelibrary.wiley.com/doi/abs/10.1111/1365-2745.1269602016nas a2200205 4500008004100000245010300041210006900144300001200213490000800225520137200233653000901605653001401614653002001628653001801648653001701666653002001683100001801703700002301721856006601744 2017 eng d00aGrazing by bison is a stronger driver of plant ecohydrology in tallgrass prairie than fire history0 aGrazing by bison is a stronger driver of plant ecohydrology in t a423-4360 v4113 a

Background and Aims: Fire and grazing are important disturbances in grasslands, yet we know little about how they impact a variety of plant physiological processes such as plant ecohydrology. Here, we assessed the impact of fire history and grazing by Bison bison on the source of water uptake and niche overlap in common grassland species at the Konza Prairie Biological Station, a temperate mesic grassland located in northeastern Kansas, USA. Methods: We used the stable isotopic signature of soil and xylem water to evaluate water uptake in Andropogo n gerardii, Vernonia baldwinii, Amorpha canescens,and Rhus glabra within varying grazing (grazed, ungrazed), fire (0,1,2 or 3 years since last burn), topography (upland, lowland), and month (July, August) contrasts over 3 years (2013–2015). Results: The presence of grazers, not fire history, altered water uptake patterns in these common grassland species. Particularly, grazing increased the proportion of shallow water utilized by A. gerardii and R. glabra, reducing niche overlap with other co-occurring species. However, these responses varied intra-annually and were often modulated by topography. Conclusions: These results suggest that grazing can alter aspects of grassland ecohydrology at small scales, which may extend to impact community and ecosystem processes at larger spatial scales.

10afire10aHerbivory10aMesic grassland10aNiche overlap10aSource water10aStable isotopes1 aO’Keefe, K.1 aNippert, Jesse, B. uhttps://link.springer.com/article/10.1007%2Fs11104-016-3048-103030nas a2200181 4500008004100000245010200041210006900143300001200212490000700224520241900231100001802650700002102668700002402689700002202713700001702735700002302752856007302775 2017 eng d00aThe interactive effects of press/pulse intensity and duration on regime shifts at multiple scales0 ainteractive effects of presspulse intensity and duration on regi a198-2180 v873 a

Regime shifts are difficult to reverse transitions that occur when an ecosystem reorganizes around a new set of self-reinforcing feedbacks. Regime shifts are predicted to occur when the intensity of some exogenous driver variable—such as temperature, annual harvest rate or nutrient addition rate—gradually approaches and crosses a threshold value, initiating a transition to an alternative state. However, many driver variables now change rapidly as presses or pulses, not gradually, requiring new conceptual frameworks for understanding and predicting regime shifts. We argue that identifying and controlling regime shifts in response to presses and pulses will require a greater focus on the duration, not just intensity, of changes in driver variables. In ecosystems with slower dynamics, transitions to an alternative state can take years to decades and as a result, a driver press with an intensity capable of resulting in a regime shift over long time-spans may fail to cause a regime shift when applied for shorter durations. We illustrate these ideas using simulations of local-scale alternative stable state models and preliminary evidence from long-term grazing and eutrophication experiments. The simulations also suggest that small changes in the duration of driver presses or pulses can determine whether an ecosystem recovers to its original state. These insights may extend to larger scales. In spatially extended simulations that included patchiness, spatial heterogeneity, and spatial connectivity, all patches recovered to their original state after shorter presses. However, once press duration exceeded a threshold, growing proportions of the landscape shifted to an alternative state as press duration increased. We observed similar patchy transitions in a catchment-scale experiment that reinstated frequent fires approximately halfway through a regime shift from grassland to shrubland, initiated by fire suppression. In both the local- and larger-scale models, the threshold duration needed to elicit regime shifts decreased as press intensity increased or when factors counteracting regime shifts weakened. These multiple lines of evidence suggest that conceptualizing regime shifts as an interactive function of the intensity and duration of driver changes will increase understanding of the varying effects of driver presses, pulses, and cycles on ecosystem dynamics.

1 aRatajczak, Z.1 aD'Odorico, Paolo1 aCollins, Scott., L.1 aBestelmeyer, B.T.1 aIsbell, F.L.1 aNippert, Jesse, B. uhttps://esajournals.onlinelibrary.wiley.com/doi/abs/10.1002/ecm.124903192nas a2200193 4500008004100000245007400041210006900115260004300184490001400227520256300241653001902804653002602823653001802849653001502867653002202882100001802904700002302922856005302945 2017 eng d00aPhysiological and morphological responses of grass species to drought0 aPhysiological and morphological responses of grass species to dr aManhattan, KSbKansas State University0 vMS Thesis3 a

The impacts of climate change over the next 100 years on North American grasslands are unknown. Climate change is projected to increase rainfall and seasonal temperature variability, leading to increased frequency of drought and decreased rainfall amounts for many grassland locations in the central Great Plains of North America. To increase our ability to predict the effects of a changing climate, I measured multiple morphological and physiological responses from a diverse suite of C3 and C4 grasses. Due to varying characteristics associated with the different photosynthetic pathways, these grass species respond differently to altered temperature and precipitation. I monitored grass physiology and microanatomy in conjunction with varying watered availability to replicate drought. In the second chapter, I observed leaf-level physiology and root level morphology of C3 and C4 grasses when exposed to 100% water reduction. Results indicated that response to water reduction are not always dependent on the photosynthetic pathway. Root-level morphological measurements were found to vary significantly between species in the same genus; F. ovina had the highest specific root length (SRL), which is an indicator of tolerance to environmental variability. Results also indicated that grasses of interest have thresholds that when passed result in a photosynthetically inactive plant; however it was shown that they are able to recover to near pre-drought gas exchange rates when water is re-applied. The third chapter investigated both leaf-level physiology and morphology in dominant C4¬ grasses across Kansas’ rainfall gradient over the growing season. I hypothesized that variation within a species’ physiology would be greater than its’ morphology. I also hypothesized that morphology would predict variability in a species physiological response to changes in climate. This research discovered within a location and species, leaf morphology is fixed across the growing season. Strong correlations between leaf physiology and morphology were observed, however, the strength and relationship changed among the species compared. A. gerardii and P. virgatum exhibited opposing relationships when comparing their photosynthetic rates to the amount of bundle sheath cells. This result highlights strong species-specific relationship between physiology and morphology. My results illustrate the importance of utilizing plant physiology and morphology to understand how grasses may respond to future climate change scenarios.

10aClimate change10aDrought; Great Plains10aEcophysiology10aGrasslands10atallgrass prairie1 aBachle, Seton1 aNippert, Jesse, B. uhttp://krex.k-state.edu/dspace/handle/2097/3618802806nas a2200253 4500008004100000245012700041210006900168300001400237490000700251520198600258653002402244653001602268653002102284653001802305653001502323653001902338100001802357700001902375700001702394700001502411700002302426700002002449856008302469 2016 eng d00aAssessing the potential for transitions from tallgrass prairie to woodlands: are we operating beyond critical transitions?0 aAssessing the potential for transitions from tallgrass prairie t a280–2870 v693 a

A growing body of evidence suggests humans are pushing ecosystems near or beyond key ecological thresholds, resulting in transitions to new, sometimes undesirable phases or states that are costly to reverse. We used remotely sensed fire data to assess if the Flint Hills—a landscape of tallgrass prairie in the Central Great Plains, United States—is operating beyond fire frequency thresholds. Long-term fire experiments and observational evidence suggests that applying prescribed fire at return intervals > 3 yr can lead to transitions from grassland to shrubland. Fire return intervals > 10 yr and complete fire suppression, in particular, can result in transitions to woodlands over 30 − 50 yr. Once shrublands and woodlands are established, restoration back to grassland is difficult with prescribed fires. We applied these fire frequency cutoffs to remotely sensed fire data from 2000 to 2010 in the Flint Hills, identifying the extent of tallgrass prairie susceptible to shrub and tree expansion. We found that 56% (15 620 km2) of grasslands in this region are burned less than every 3 yr and are therefore susceptible to conversion to shrub or tree dominance. The potential effects of this large-scale shift are greater risk for evergreen (Juniperus virginiana) woodland fires, reduced grazing potential, and increased abundance of woodland adapted species at the expense of the native grassland biota. Of the 12 127-km2 area likely to remain grassland, 43% is burned approximately annually, contributing to vegetative homogenization and potential air-quality issues. While this synthesis forecasts a precarious future for tallgrass prairie conservation and their ecosystem services, increases in shrub or tree dominances are usually reversible until fire frequency has been reduced for more than 20 yr. This delay leaves a small window of opportunity to return fire to the landscape and avoid large-scale transformation of tallgrass prairie.

10acatastrophic shifts10aforecasting10amesic grasslands10aregime shifts10aresilience10atipping points1 aRatajczak, Z.1 aBriggs, J., M.1 aGoodin, D.G.1 aMohler, R.1 aNippert, Jesse, B.1 aObermeyer, B.K. uhttps://www.sciencedirect.com/science/article/pii/S1550742416300021?via%3Dihub02539nas a2200217 4500008004100000245010700041210006900148300001200217490000800229520184000237653001802077653002002095653001902115653002602134653001802160653002302178100001502201700001602216700002302232856006602255 2016 eng d00aComparative ecohydrology between Cornus drummondii and Solidago canadensis in upland tallgrass prairie0 aComparative ecohydrology between Cornus drummondii and Solidago  a267-2760 v2173 a

Woody species expansion threatens to transform mesic North American grasslands. In many tallgrass prairies of the central Great Plains with deep soil, Cornus drummondii develops large shrub islands that exhibit non-linear increases in cover through time. Reliance on soil moisture from deeper soil depths facilitates constant gas exchange rates and minimizes competition with coexisting herbaceous species. Conversely, C. drummondii growth and expansion in thin-soil locations is stochastic and these locations are typically free of large shrub islands. At the Konza Prairie in northeast Kansas, USA, we compared the ecohydrology of C. drummondii individuals to a similar-sized forb (Solidago canadensis) in thin-soil locations with varying fire frequency (4-, 20-year) and grazer abundance (bison present or absent). Gas exchange rates were relatively constant for C. drummondii, while S. canadensis declined across the growing season. For S. canadensis, maximum photosynthesis (Amax), daytime transpiration (E), and stomatal conductance (gs) were higher on ungrazed than grazed treatments. Nighttime E rates were higher in C. drummondii, accounting for over 10 % of the daytime E rates. The water source used did not vary among contrasts, with the majority of water uptake occurring from 30 cm depth for both species. These results highlight a unique ecohydrology of C. drummondii (static water flux, and high rates of nighttime E) compared to a similar-sized, co-occurring forb. Whereas C. drummondii is infrequent in thin-soil locations, the climate conditions occurring during measurements were not a likely filter restricting persistence. Rather, drier conditions or interactions with other grassland disturbances are likely required to restrict C. drummondii encroachment in the thins-soil locations of tallgrass prairie.

10aKonza Prairie10aMesic grassland10aphotosynthesis10aStable water isotopes10aTranspiration10awoody encroachment1 aMuench, A.1 aO'Keefe, K.1 aNippert, Jesse, B. uhttps://link.springer.com/article/10.1007%2Fs11258-016-0567-z02240nas a2200157 4500008004100000245012900041210006900170300001700239490000600256520167900262100001701941700001901958700002301977700001902000856006302019 2016 eng d00aForaging decisions underlying restricted space use: effects of fire and forage maturation on large herbivore nutrient uptake0 aForaging decisions underlying restricted space use effects of fi a5843–5853 0 v63 a

Recent models suggest that herbivores optimize nutrient intake by selecting patches of low to intermediate vegetation biomass. We assessed the application of this hypothesis to plains bison (Bison bison) in an experimental grassland managed with fire by estimating daily rates of nutrient intake in relation to grass biomass and by measuring patch selection in experimental watersheds in which grass biomass was manipulated by prescribed burning. Digestible crude protein content of grass declined linearly with increasing biomass, and the mean digestible protein content relative to grass biomass was greater in burned watersheds than watersheds not burned that spring (intercept; F1,251 = 50.57, P < 0.0001). Linking these values to published functional response parameters, ad libitum protein intake, and protein expenditure parameters, Fryxell's (Am. Nat., 1991, 138, 478) model predicted that the daily rate of protein intake should be highest when bison feed in grasslands with 400–600 kg/ha. In burned grassland sites, where bison spend most of their time, availability of grass biomass ranged between 40 and 3650 kg/ha, bison selected foraging areas of roughly 690 kg/ha, close to the value for protein intake maximization predicted by the model. The seasonal net protein intake predicted for large grazers in this study suggest feeding in burned grassland can be more beneficial for nutrient uptake relative to unburned grassland as long as grass regrowth is possible. Foraging site selection for grass patches of low to intermediate biomass help explain patterns of uniform space use reported previously for large grazers in fire-prone systems.

1 aRaynor, E.J.1 aJoern, Anthony1 aNippert, Jesse, B.1 aBriggs, J., M. uhttps://onlinelibrary.wiley.com/doi/full/10.1002/ece3.230403518nas a2200193 4500008004100000245010400041210006900145260004300214490002100257520286800278653001503146653001303161653002103174653001303195653001803208100002203226700002303248856005303271 2016 eng d00aPatterns and ecological consequences of water uptake, redistribution, and loss in tallgrass prairie0 aPatterns and ecological consequences of water uptake redistribut aManhattan, KSbKansas State University0 vPhD Dissertation3 a

Water availability is a key driver of many plant and ecosystem processes in tallgrass prairies, yet we have a limited understanding of how grassland plants utilize water through space and time. Considering that tallgrass prairies experience tremendous heterogeneity in soil resources, identifying spatiotemporal variation in plant ecohydrology is critical for understanding current drivers of plant responses to water and for predicting ecosystem responses to future changes in climate. Here, I investigated the patterns, drivers, and ecological consequences of plant water use (e.g., water uptake, water redistribution, and water loss) in a native tallgrass prairie located in northeastern Kansas, USA. Using a combination of leaf gas exchange, sap flow, and isotopic techniques, I addressed four main questions: 1) How does fire and grazing by bison impact use of water from different sources and niche overlap for common grasses, forbs, and shrubs? 2) Does hydraulic lift occur in grazed and ungrazed tallgrass prairie, and does this impact facilitation for water within grassland communities? 3) What are the patterns and drivers of nocturnal transpiration in common grassland species? 4) How does diel stem sap flow and canopy transpiration vary among common grassland species?

I found that bison grazing increased the depth of water uptake by Andropogon gerardii and Rhus glabra, reducing niche overlap with co-occurring species. Conversely, grazing did not affect hydraulic lift, which was generally uncommon and likely limited by nocturnal transpiration. Further, leaf gas exchange measurements indicated that nocturnal transpiration occurred commonly in tallgrass prairie plants and was greatest among grasses and early in the growing season. Nocturnal transpiration was not driven by vapor pressure deficit or soil moisture, as commonly observed in other systems, but was regulated by nocturnal stomatal conductance in most species. Finally, I found that daytime sap flow rates were variable among species and functional types, with larger flux rates among woody species. Nocturnal sap flow rates were more consistent across species, which caused nighttime sap flow and transpiration to account for a larger proportion of daily flux rates in grasses than in forbs or shrubs. These results show that water uptake, water redistribution, and water loss are all influenced by different biotic and abiotic drivers and have varying ecological impacts across a heterogeneous landscape. Additionally, extensive differences in water flux exist among co-occurring species and plant functional groups, which likely reflect varying strategies to tolerate water limitation. These results suggest that shifts in the abundance of these species with future climate changes, or with ecosystem state changes, will likely impact ecosystem-level water balance.

10aGrasslands10aIsotopes10aPlant physiology10aSap flow10aTranspiration1 aO'Keefe, Kimberly1 aNippert, Jesse, B. uhttp://krex.k-state.edu/dspace/handle/2097/3451401992nas a2200145 4500008004100000245016200041210006900203300001100272490000800283520141700291100002401708700002301732700002401755856006701779 2016 eng d00aA safety vs efficiency trade-off identified in the hydraulic pathway of grass leaves is decoupled from photosynthesis, stomatal conductance and precipitation0 asafety vs efficiency tradeoff identified in the hydraulic pathwa a97-1070 v2103 a

A common theme in plant physiological research is the trade-off between stress tolerance and growth; an example of this trade-off at the tissue level is the safety vs efficiency hypothesis, which suggests that plants with the greatest resistance to hydraulic failure should have low maximum hydraulic conductance. Here, we quantified the leaf-level drought tolerance of nine C4 grasses as the leaf water potential at which plants lost 50% (P50 × RR ) of maximum leaf hydraulic conductance (Ksat ), and compared this trait with other leaf-level and whole-plant functions. We found a clear trade-off between Ksat and P50 × RR when Ksat was normalized by leaf area and mass (P = 0.05 and 0.01, respectively). However, no trade-off existed between P50 × RR and gas-exchange rates; rather, there was a positive relationship between P50 × RR and photosynthesis (P = 0.08). P50 × RR was not correlated with species distributions based on precipitation (P = 0.70), but was correlated with temperature during the wettest quarter of the year (P < 0.01). These results suggest a trade-off between safety and efficiency in the hydraulic system of grass leaves, which can be decoupled from other leaf-level functions. The unique physiology of C4 plants and adaptations to pulse-driven systems may provide mechanisms that could decouple hydraulic conductance from other plant functions.

1 aOcheltree, Troy, W.1 aNippert, Jesse, B.1 aPrasad, P., V. Vara uhttps://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.1378102215nas a2200241 4500008004100000022001400041245012300055210006900178300001400247490000800261520148100269653001801750653000901768653001401777653001201791653001401803100001601817700002301833700001801856700001501874700001801889856006601907 2016 eng d a0029-854900aTight coupling of leaf area index to canopy nitrogen and phosphorus across heterogeneous tallgrass prairie communities0 aTight coupling of leaf area index to canopy nitrogen and phospho a889 - 8980 v1823 a

Nitrogen (N) and phosphorus (P) are limiting nutrients for many plant communities worldwide. Foliar N and P along with leaf area are among the most important controls on photosynthesis and hence productivity. However, foliar N and P are typically assessed as species level traits, whereas productivity is often measured at the community scale. Here, we compared the community-level traits of leaf area index (LAI) to total foliar nitrogen (TFN) and total foliar phosphorus (TFP) across nearly three orders of magnitude LAI in grazed and ungrazed tallgrass prairie in north-eastern Kansas, USA. LAI was strongly correlated with both TFN and TFP across communities, and also within plant functional types (grass, forb, woody, and sedge) and grazing treatments (bison or cattle, and ungrazed). Across almost the entire range of LAI values and contrasting communities, TFN:TFP ratios indicated co-limitation by N and P in almost all communities; this may further indicate a community scale trend of an optimal N and P allocation per unit leaf area for growth. Previously, results from the arctic showed similar tight relationships between LAI:TFN, suggesting N is supplied to canopies to maximize photosynthesis per unit leaf area. This tight coupling between LAI, N, and P in tallgrass prairie suggests a process of optimal allocation of N and P, wherein LAI remains similarly constrained by N and P despite differences in species composition, grazing, and canopy density.

10aCo-limitation10afire10agrassland10agrazers10anutrients1 aKlodd, A.E.1 aNippert, Jesse, B.1 aRatajczak, Z.1 aWaring, H.1 aPhoenix, G.K. uhttps://link.springer.com/article/10.1007%2Fs00442-016-3713-302159nas a2200145 4500008004100000245007800041210006900119300001400188490000700202520166800209100002301877700001801900700001401918856008101932 2015 eng d00aChallenging the maximum rooting depth paradigm in grasslands and savannas0 aChallenging the maximum rooting depth paradigm in grasslands and a739 - 7450 v293 a
  1. For many grassland and savanna ecosystems, water limitation is a key regulator of individual plant, community and ecosystem processes. Maximum rooting depth is commonly used to characterize the susceptibility of plant species to drought. This rests on the assumption that deep-rooted plant species would have a greater total volume of soil water to exploit and should be less susceptible to episodic changes in water availability.
  2. Independent of maximum rooting depth, rooting strategies based on differences in biomass allocation with depth, uptake plasticity in relation to water availability and variation in water transport capability may all influence growth responses and susceptibility to drought. Many examples from grasslands and savannas reflect these rooting strategies among coexisting grass, forb and woody species.
  3. Here, we use a dynamic model of plant water uptake and growth to show how changes in root distribution, functional plasticity and root hydraulic conductivity have the potential to influence aboveground biomass and competitive outcomes, even when maximum rooting depth remains constant. We also show theoretically that shifts in root distribution to surface soils without changes in maximum depth can potentially outweigh the benefits of increased maximum rooting depth.
  4. Combining our current reliance on biogeographic descriptions of maximum rooting depth with insights about other, more subtle aspects of root structure and function are likely to improve our understanding of ecosystem responses to dynamic water limitation.
1 aNippert, Jesse, B.1 aHoldo, R., M.1 aSayer, E. uhttps://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2435.1239002244nas a2200145 4500008004100000245012200041210006900163300001500232490000700247520170900254100001801963700002301981700002002004856007402024 2014 eng d00aAbrupt transition of mesic grassland to shrubland: evidence for thresholds, alternative attractors, and regime shifts0 aAbrupt transition of mesic grassland to shrubland evidence for t a2633 -26450 v953 a

Ecosystems with alternative attractors are susceptible to abrupt regime shifts that are often difficult to predict and reverse. In this study, we quantify multiple system dynamics to determine whether the transition of mesic grassland to shrubland, a widespread phenomenon, represents a linear reversible process, a nonlinear but reversible threshold process, or a transition between alternative attractors that is nonlinear and prone to hysteresis. Using a 28-yr data set with annual resolution and extensive spatial replication, we found that shrub cover is correlated with distinct thresholds of fire and C4 grass cover, resulting in temporal bimodality of shrub cover and abrupt shifts of shrub cover despite gradual changes in grass cover. These abrupt increases in shrub cover are the most rapid ever reported in grasslands, and illustrate internal thresholds that separate grasslands and shrublands. Nonlinear transitions from low to high shrub cover were also closely associated with positive feedback mechanisms that alter fire and competition (r2 = 0.65), suggesting that grasslands and shrublands could show hysteresis, and by definition exist as alternative attractors. Thus, the response of this ecosystem to anthropogenic activity should tend to be rapid, nonlinear, and perhaps difficult to reverse. Regime shifts in this mesic grassland were predictable: we found that grassland and shrubland attractors were differentiated by critical thresholds of ∼50–70% grass cover, 5–10% shrub cover, and a fire return interval of ∼3 yr. These thresholds may provide adaptive potential for managing nonlinear behavior in socio-ecological systems in a changing environment.

1 aRatajczak, Z.1 aNippert, Jesse, B.1 aOcheltree, T.W. uhttps://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/13-1369.102581nas a2200217 4500008004100000245007000041210006900111300001100180490000700191520192800198653002802126653001702154653002302171653000902194653001802203653001802221653001802239100001702257700002302274856006602297 2014 eng d00aCessation of burning dries soils long-term in a tallgrass prairie0 aCessation of burning dries soils longterm in a tallgrass prairie a54 -650 v173 a

Soil moisture is a critical variable in grassland function, yet how fire regimes influence ecohydrology is poorly understood. By altering productivity, species composition, and litter accumulation, fire can indirectly increase or decrease soil water depletion on a range of time scales and depths in the soil profile. To better understand how fire influences soil moisture in grasslands, we analyzed 28 years of soil moisture data from two watersheds in a central North American grassland which differ in their long-term fire frequency. Across 28 years, cessation of prescribed burning initially led to wetter soils, likely as litter accumulated and both transpiration and evaporation were suppressed. Long-term, cessation of burning led to soils drying more, especially at depths greater than 75 cm. The long-term drying of deep soils is consistent with the increase in woody species in the infrequently burned grassland as woody species likely have a greater reliance on soil water from deeper soil layers compared to co-occurring herbaceous species. Despite the ecohydrological changes associated with the cessation of prescribed burning, watersheds with different burn regimes responded similarly to short-term variation in climate variation. In both watersheds, low precipitation and high temperatures led to drier soils with greater responses in soil moisture to climate variation later in the season than earlier. There is no current evidence that the cessation of burning in this ecosystem will qualitatively alter how evapotranspiration responds to climate variation, but the use of deeper soil water by woody plants has the potential for greater transpiration during dry times. In all, modeling the depth-specific responses of soil moisture and associated ecosystem processes to changes in burn regimes will likely require including responses of plant community composition over short and long time scales.

10acritical climate period10aecohydrology10aEvapotranspiration10afire10aKonza Prairie10asoil moisture10awoody species1 aCraine, J.M.1 aNippert, Jesse, B. uhttps://link.springer.com/article/10.1007%2Fs10021-013-9706-801971nas a2200133 4500008004100000245009800041210006900139260004300208490002300251520148500274100001801759700002301777856003701800 2014 eng d00aEcological thresholds and abrupt transitions of tallgrass prairie to shrublands and woodlands0 aEcological thresholds and abrupt transitions of tallgrass prairi aManhattan, KSbKansas State University0 v PhD. Dissertation3 a

Ecological thresholds are breakpoints where small increases in external pressure can generate rapid and difficult to reverse ecological transitions. Often, ecological thresholds are not recognized until they are crossed at a large-scale, leading to unintended and lasting externalities. In tallgrass prairie, we identified ecological thresholds of 3-year fire returns and ~60% grass cover, based on mechanistic field studies and long-term fire and grazing experiments. When tallgrass prairie is pushed passed these thresholds, it makes an abrupt transition to a self-reinforcing shrubland state. Demographic bottlenecks, niche partitioning, and altered fire feedback mechanisms account for both the non-linear nature of grassland-shrubland transitions and the resistance of established shrublands to fire and drought. In the last decade, only ~27% of Central Great Plains tallgrass prairie was burned every 1-2 years, and therefore ~73% of this region is susceptible to shrubland and woodland transitions in the next two to three decades. If transitions to shrublands and woodlands do occur, we expect a multi-trophic loss of grassland biodiversity, decreased cattle production, and the potential for damaging woodland fires in close proximity to human development. However, knowledge of fire thresholds, adaptive management tools, and bottom-up citizen action campaigns are creating a rare window of opportunity to avoid transformation of the remaining tallgrass prairies.

1 aRatajczak, Z.1 aNippert, Jesse, B. uhttp://hdl.handle.net/2097/1766102633nas a2200253 4500008004100000245013900041210006900180300001500249490000800264520182600272653001002098653001502108653001202123653001502135653001202150653003102162653001002193653001502203100001802218700002302236700001902259700002002278856008102298 2014 eng d00aFire dynamics distinguish grasslands, shrublands, and woodlands as alternative attractors in the Central Great Plains of North America0 aFire dynamics distinguish grasslands shrublands and woodlands as a1374 -13850 v1023 a

Grasslands are threatened globally due to the expansion of woody plants. The few remaining headwater streams within tallgrass prairies are becoming more like typical forested streams due to rapid conversion of riparian zones from grassy to wooded. Forestation can alter stream hydrology and biogeochemistry. We estimated the rate of riparian woody plant expansion within a 30 m buffer zone surrounding the stream bed across whole watersheds at Konza Prairie Biological Station over 25 years from aerial photographs. Watersheds varied with respect to experimentally-controlled fire and bison grazing. Fire frequency, presence or absence of grazing bison, and the historical presence of woody vegetation prior to the study time period (a proxy for proximity of propagule sources) were used as independent variables to predict the rate of riparian woody plant expansion between 1985 and 2010. Water yield was estimated across these years for a subset of watersheds. Riparian woody encroachment rates increased as burning became less frequent than every two years. However, a higher fire frequency (1–2 years) did not reverse riparian woody encroachment regardless of whether woody vegetation was present or not before burning regimes were initiated. Although riparian woody vegetation cover increased over time, annual total precipitation and average annual temperature were variable. So, water yield over 4 watersheds under differing burn frequencies was quite variable and with no statistically significant detected temporal trends. Overall, burning regimes with a frequency of every 1–2 years will slow the conversion of tallgrass prairie stream ecosystems to forested ones, yet over long time periods, riparian woody plant encroachment may not be prevented by fire alone, regardless of fire frequency.

10abison10aEcosystems10aForests10aGrasslands10aGrazing10aLinear regression analysis10aTrees10aWatersheds1 aRatajczak, Z.1 aNippert, Jesse, B.1 aBriggs, J., M.1 aBlair, John, M. uhttps://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2745.1231100428nas a2200157 4500008004100000245002200041210002200063260003800085300001200123490000600135100002000141700002300161700001900184700001400203856005300217 2014 eng d00aGrassland Ecology0 aGrassland Ecology bSpringer-Verlag Berlin Heidelberg a389-4230 v81 aBlair, John, M.1 aNippert, Jesse, B.1 aBriggs, J., M.1 aMonson, R uhttp://knz.lternet.edu/content/grassland-ecology01833nas a2200145 4500008004100000245009700041210006900138300001500207490000600222520134300228100001701571700002301588700001501611856006101626 2014 eng d00aImpacts of seasonality and surface heterogeneity on water-use efficiency in mesic grasslands0 aImpacts of seasonality and surface heterogeneity on wateruse eff a1223 -12330 v73 a

Woody encroachment is occurring in grasslands worldwide, with largely unknown effects on local carbon and water fluxes and the energy balance. Water-use efficiency (λ) is a measure of carbon assimilation per evapotranspiration. Here, a was compared among three different grassland ecosystems in eastern KS, USA, by using the eddy covariance technique. Variation in λ was examined at multiple timescales and across different burning regimes. Site-specific variations in λ were more readily observed at seasonal and inter-annual timescales rather than daily and monthly averages. Annually burned grassland with homogeneous C4 grass cover had less negative values of λ [lower water-use efficiency (WUE)] than infrequently burned grassland that is presently undergoing woody encroachment and a transition to a shrub-dominated ecosystem. The most likely explanation for differences in λ are differences in rooting depth and source-water acquisition between encroaching woody plants and the native grass community. Reliance on a deeper water source by the woody community may buffer the negative consequences of forecasted climate variability and drought, resulting in greater landscape WUE and reduced susceptibility to water stress when compared with the coexisting grass species. Copyright © 2013 John Wiley & Sons, Ltd.

1 aBrunsell, N.1 aNippert, Jesse, B.1 aBuck, T.L. uhttps://onlinelibrary.wiley.com/doi/abs/10.1002/eco.145501891nas a2200157 4500008004100000245007400041210006900115300001500184490000700199520137200206100002101578700001701599700002301616700002001639856007401659 2014 eng d00aLack of eutrophication in a tallgrass prairie ecosystem over 27 years0 aLack of eutrophication in a tallgrass prairie ecosystem over 27  a1225 -12350 v953 a

Many North American grasslands are receiving atmospheric nitrogen (N) deposition at rates above what are considered critical eutrophication thresholds. Yet, potential changes in grassland function due to anthropogenic N deposition are poorly resolved, especially considering that other dynamic factors such as land use and precipitation can also affect N availability. To better understand whether elevated N deposition has altered ecosystem structure or function in North American grasslands, we analyzed a 27-year record of ecophysiological, community, and ecosystem metrics for an annually burned Kansas tallgrass prairie. Over this time, despite increasing rates of N deposition that are within the range of critical loads for grasslands, there was no evidence of eutrophication. Plant N concentrations did not increase, soil moisture did not decline, forb diversity did not decline, and the relative abundance of dominant grasses did not shift toward more eutrophic species. Neither aboveground primary productivity nor N availability to plants increased. The fates of deposited N in grasslands are still uncertain, and could include management losses through burning and grazing. However, evidence from this grassland indicates that eutrophication of North American grassland ecosystems is not an inevitable consequence of current levels of N deposition.

1 aMcLauchlan, K.K.1 aCraine, J.M.1 aNippert, Jesse, B.1 aOcheltree, T.W. uhttps://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/13-1068.101773nas a2200145 4500008004100000245012100041210006900162300001300231490000700244520125100251100002001502700002301522700001901545856006301564 2014 eng d00aStomatal responses to changes in vapor pressure deficit reflect tissue-specific differences in hydraulic conductance0 aStomatal responses to changes in vapor pressure deficit reflect  a132 -1390 v373 a

The vapor pressure deficit (D) of the atmosphere can negatively affect plant growth as plants reduce stomatal conductance to water vapor (gwv) in response to increasing D, limiting the ability of plants to assimilate carbon. The sensitivity of gwv to changes in D varies among species and has been correlated with the hydraulic conductance of leaves (Kleaf), but the hydraulic conductance of other tissues has also been implicated in plant responses to changing D. Among the 19 grass species, we found that Kleaf was correlated with the hydraulic conductance of large longitudinal veins (Klv, r2 = 0.81), but was not related to Kroot (r2 = 0.01). Stomatal sensitivity to D was correlated with Kleaf relative to total leaf area (r2 = 0.50), and did not differ between C3 and C4 species. Transpiration (E) increased in response to D, but 8 of the 19 plants showed a decline in E at high D, indicative of an ‘apparent feedforward’ response. For these individuals, E began to decline at lower values of D in plants with low Kroot (r2 = 0.72). These results show the significance of both leaf and root hydraulic conductance as drivers of plant responses to evaporative demand.

1 aOcheltree, T.W.1 aNippert, Jesse, B.1 aPrasad, P.V.V. uhttps://onlinelibrary.wiley.com/doi/full/10.1111/pce.1213702826nas a2200277 4500008004100000245010400041210006900145300001200214490000600226520201300232653001502245653001502260653001202275653001102287653002102298653001202319653001102331653002002342100002302362700002002385700001702405700001802422700001302440700001702453856007802470 2013 eng d00aEvidence of physiological decoupling from grassland ecosystem drivers by an encroaching woody shrub0 aEvidence of physiological decoupling from grassland ecosystem dr a81630 -0 v83 a

Shrub encroachment of grasslands is a transformative ecological process by which native woody species increase in cover and frequency and replace the herbaceous community. Mechanisms of encroachment are typically assessed using temporal data or experimental manipulations, with few large spatial assessments of shrub physiology. In a mesic grassland in North America, we measured inter- and intra-annual variability in leaf δ13C in Cornus drummondii across a grassland landscape with varying fire frequency, presence of large grazers and topographic variability. This assessment of changes in individual shrub physiology is the largest spatial and temporal assessment recorded to date. Despite a doubling of annual rainfall (in 2008 versus 2011), leaf δ13C was statistically similar among and within years from 2008-11 (range of −28 to −27‰). A topography*grazing interaction was present, with higher leaf δ13C in locations that typically have more bare soil and higher sensible heat in the growing season (upland topographic positions and grazed grasslands). Leaf δ13C from slopes varied among grazing contrasts, with upland and slope leaf δ13C more similar in ungrazed locations, while slopes and lowlands were more similar in grazed locations. In 2011, canopy greenness (normalized difference vegetation index – NDVI) was assessed at the centroid of individual shrubs using high-resolution hyperspectral imagery. Canopy greenness was highest mid-summer, likely reflecting temporal periods when C assimilation rates were highest. Similar to patterns seen in leaf δ13C, NDVI was highest in locations that typically experience lowest sensible heat (lowlands and ungrazed). The ability of Cornus drummondii to decouple leaf physiological responses from climate variability and fire frequency is a likely contributor to the increase in cover and frequency of this shrub species in mesic grassland and may be generalizable to other grasslands undergoing woody encroachment.

10aEcosystems10aGrasslands10aGrazing10aLeaves10aPlant physiology10aSeasons10aShrubs10aWater resources1 aNippert, Jesse, B.1 aOcheltree, T.W.1 aOrozco, G.L.1 aRatajczak, Z.1 aLing, B.1 aSkibbe, A.M. uhttps://journals.plos.org/plosone/article?id=10.1371/journal.pone.008163002135nas a2200229 4500008004100000245008200041210006900123300001100192490000600203520145700209653002701666653001201693653002201705100001701727700002001744700002301764700001601787700001701803700001701820700001901837856004901856 2013 eng d00aGlobal diversity of drought tolerance and grassland climate-change resilience0 aGlobal diversity of drought tolerance and grassland climatechang a63 -670 v33 a

Drought reduces plant productivity, induces widespread plant mortality and limits the geographic distribution of plant species1, 2, 3, 4, 5, 6, 7. As climates warm and precipitation patterns shift in the future8, 9, understanding the distribution of the diversity of plant drought tolerance is central to predicting future ecosystem function and resilience to climate change10, 11, 12. These questions are especially pressing for the world’s 11,000 grass species13, which dominate a large fraction of the terrestrial biosphere14, yet are poorly characterized with respect to responses to drought. Here, we show that physiological drought tolerance, which varied tenfold among 426 grass species, is well distributed both climatically and phylogenetically, suggesting most native grasslands are likely to contain a high diversity of drought tolerance. Consequently, local species may help maintain ecosystem functioning in response to changing drought regimes without requiring long-distance migrations of grass species. Furthermore, physiologically drought-tolerant species had higher rates of water and carbon dioxide exchange than intolerant species, indicating that severe droughts may generate legacies for ecosystem functioning. In all, our findings suggest that diverse grasslands throughout the globe have the potential to be resilient to drought in the face of climate change through the local expansion of drought-tolerant species.

10aClimate-change ecology10aDrought10aGrassland ecology1 aCraine, J.M.1 aOcheltree, T.W.1 aNippert, Jesse, B.1 aTowne, E.G.1 aSkibbe, A.M.1 aKembel, S.W.1 aFargione, J.E. uhttps://www.nature.com/articles/nclimate163402035nas a2200169 4500008004100000245010400041210006900145300000900214490000600223520145600229100002301685700002301708700001701731700002001748700001901768856007801787 2013 eng d00aIdentifying the water sources consumed by bison: implications for large mammalian grazers worldwide0 aIdentifying the water sources consumed by bison implications for a23 -0 v43 a

The sources of drinking water consumed by grazers vary over time and may be highly selective, similar to choices in diet. Water sources consumed by large grazers in natural populations are not typically measured directly. Instead, consumption is inferred based on animal proximity to water sources. Here, we analysed the stable isotopic signature of water (δ18O and δD) extracted from fecal samples from a herd of bison in mesic grassland as a direct estimation of the water sources consumed over time. Bison at this site have their choice of a range of habitats and drinking water sources. Potential source-water samples measured had a large range of isotopic signatures, allowing the isotopic composition of water from bison fecal samples to be proportionally estimated based on varying sources. Results indicate bison have low reliance on multiple streams on site; rather, the majority of water consumed was from rainfall-fed sources (puddles and wallows) and from forage. Our research suggests that source-water analysis from fecal samples is a robust technique when samples from large grazers can be collected soon after production. These results have implications for analyses of the foraging patterns and landscape utilization by this and other large grazers, because hotter and drier future conditions are likely to reduce the frequency and amount of rainfall-fed puddles available for consumption in many grassland systems worldwide.

1 aNippert, Jesse, B.1 aCulbertson, T.S.F.1 aOrozco, G.L.1 aOcheltree, T.W.1 aHelliker, B.R. uhttps://esajournals.onlinelibrary.wiley.com/doi/full/10.1890/ES12-00359.102573nas a2200133 4500008004100000245013600041210006900177300001300246490000600259520205500265100001802320700002302338856007802361 2013 eng d00aPhysiological and growth responses of switchgrass (Panicum virgatum L.) in native stands under passive air temperature manipulation0 aPhysiological and growth responses of switchgrass Panicum virgat a683 -6920 v53 a

In the central Great Plains of North America, climate change predictions include increases in mean annual temperature of 1.5–5.5 °C by 2100. Ecosystem responses to increased temperatures are likely to be regulated by dominant plant species, such as the potential biofuel species Panicum virgatum (switchgrass) in the tallgrass prairie. To describe the potential physiological and whole-plant responses of this species to future changes in air temperatures, we used louvered open-sided chambers (louvered OSC; 1 × 1 m, adjustable height) to passively alter canopy temperature in native stands of P. virgatum growing in tallgrass prairie at varying topographic positions (upland/lowland). The altered temperature treatment decreased daily mean temperatures by 1 °C and maximum temperatures by 4 °C in May and June, lowered daytime stomatal conductance and transpiration, decreased tiller density, increased specific leaf area, and delayed flowering. Among topographic contrasts, aboveground biomass, flowering tiller density, and tiller weight were greater in lowland sites compared to upland sites, with no temperature treatment interactions. Differences in biomass production responded more to topography than the altered temperature treatment, as soil water status varied considerably between topographic positions. These results indicate that while water availability as a function of topography was a strong driver of plant biomass, many leaf-level physiological processes were responsive to the small decreases in daily mean and maximum temperature, irrespective of landscape position. The varying responses of leaf-level gas exchange and whole-plant growth of P. virgatum in native stands to altered air temperature or topographic position illustrate that accurately forecasting yields for P. virgatum in mixed communities will require greater integration of physiological responses to simulated climate change (increased temperature) and resource availability over natural environmental gradients (soil moisture).

1 aHartman, J.C.1 aNippert, Jesse, B. uhttps://onlinelibrary.wiley.com/doi/full/10.1111/j.1757-1707.2012.01204.x02048nas a2200157 4500008004100000245011900041210006900160300000900229490000600238520149400244100001801738700001401756700002301770700001901793856007801812 2013 eng d00aPopulation origin and genome size do not impact Panicum virgatum (switchgrass) responses to variable precipitation0 aPopulation origin and genome size do not impact Panicum virgatum a37 -0 v43 a

Population-level adaptation to broad-scale regional climates or within-population variation in genome size of the genetically and phenotypically diverse C4 grass, Panicum virgatum (switchgrass), may influence the responses of this species to future precipitation variability associated with climate change. Therefore, we investigated P. virgatum responses to water variability between natural populations collected across a latitudinal gradient and among individuals spanning a range of genomes sizes within these populations. P. virgatum plants from natural populations originating from Kansas, Oklahoma, and Texas, U.S.A, received frequent, small precipitation events (“ambient”) or infrequent, large precipitation events (“altered”) to simulate contrasting rainfall variability expected for this region. We measured leaf-level physiology, aboveground biomass and genome size for each individual. Gas exchange rates and aboveground biomass varied significantly by population origin but did not differ by genome size. Altered precipitation treatments reduced leaf-level physiological rates; however this result did not vary by population or genome size. Our results suggest that trait variation in P. virgatum is primarily attributed to population-level adaptation across a latitudinal gradient, not genome size, and that neither population-level adaptation nor genome size may be important predictors of P. virgatum responses to future climatic conditions.

1 aO’Keefe, K.1 aTomeo, N.1 aNippert, Jesse, B.1 aSpringer, C.J. uhttps://esajournals.onlinelibrary.wiley.com/doi/full/10.1890/ES12-00339.101507nas a2200157 4500008004100000245007100041210006900112300001300181490000800194520099700202100001701199700001601216700001701232700002301249856007701272 2013 eng d00aPrecipitation timing and grazer performance in a tallgrass prairie0 aPrecipitation timing and grazer performance in a tallgrass prair a191 -1980 v1223 a

Changes in precipitation amount and variability have the potential to alter the structure and function of grasslands, but we know little about how changes in the timing of precipitation might affect grasslands. Here, we analyze long-term records from a tallgrass prairie to show that shifts in the timing of precipitation during the growing season have little effect on primary productivity or grass reproduction, but can greatly affect grazer performance. While greater late-season precipitation increases the weight gain of adult and young bison, greater mid-season precipitation decreases their weight gain. In addition, calving rates are lower after years with greater mid-season precipitation and higher after years with greater late-season precipitation. As well-timed drought can actually increase grazer weight gain and reproduction, it will be necessary to generate predictions of within-season distribution of precipitation to successfully forecast future grazer performance.

1 aCraine, J.M.1 aTowne, E.G.1 aTolleson, D.1 aNippert, Jesse, B. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/j.1600-0706.2012.20400.x01677nas a2200145 4500008004100000245008900041210006900130300001500199490000700214520117000221100002001391700002301411700001901434856007801453 2012 eng d00aChanges in stomatal conductance along grass blades reflect changes in leaf structure0 aChanges in stomatal conductance along grass blades reflect chang a1040 -10490 v353 a

Identifying the consequences of grass blade morphology (long, narrow leaves) on the heterogeneity of gas exchange is fundamental to an understanding of the physiology of this growth form. We examined acropetal changes in anatomy, hydraulic conductivity and rates of gas exchange in five grass species (including C3 and C4 functional types). Both stomatal conductance and photosynthesis increased along all grass blades despite constant light availability. Hydraulic efficiency within the xylem remained constant along the leaf, but structural changes outside the xylem changed in concert with stomatal conductance. Stomatal density and stomatal pore index remained constant along grass blades but interveinal distance decreased acropetally resulting in a decreased path length for water movement from vascular bundle to stomate. The increase in stomatal conductance was correlated with the decreased path length through the leaf mesophyll. A strong correlation between the distance from vascular bundles to stomatal pores and stomatal conductance has been identified across species; our results suggest this relationship also exists within individual leaves.

1 aOcheltree, T.W.1 aNippert, Jesse, B.1 aPrasad, P.V.V. uhttps://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-3040.2011.02470.x02239nas a2200205 4500008004100000245007500041210006900116300001300185490000800198520158600206653001701792653001801809653002901827653002701856653002701883100001701910700001701927700002301944856006601967 2012 eng d00aClimate change alters growing season flux dynamics in mesic grasslands0 aClimate change alters growing season flux dynamics in mesic gras a427 -4400 v1073 a

Changing climate could affect the functioning of grassland ecosystems through variation in climate forcings and by altering the interactions of forcings with ecological processes. Both the short and long-term effects of changing forcings and ecosystem interactions are a critical part of future impacts to ecosystem ecology and hydrology. To explore these interactions and identify possible characteristics of climate change impacts to mesic grasslands, we employ a low-dimensional modeling framework to assess the IPCC A1B scenario projections for the Central Plains of the United States; forcings include increased precipitation variability, increased potential evaporation, and earlier growing season onset. These forcings are also evaluated by simulations of vegetation photosynthetic capacity to explore the seasonal characteristics of the vegetation carbon assimilation response for species at the Konza Prairie in North Central Kansas, USA. The climate change simulations show decreases in mean annual soil moisture and and carbon assimilation and increased variation in water and carbon fluxes during the growing season. Simulations of the vegetation response show increased variation at the species-level instead of at a larger class scale, with important heterogeneity in how individual species respond to climate forcings. Understanding the drivers and relationships behind these ecosystem responses is important for understanding the likely scale of climate change impacts and for exploring the mechanisms shaping growing season dynamics in grassland ecosystems.

10aecohydrology10aKonza Prairie10aLow-dimensional modeling10aNonlinear interactions10aSoil moisture feedback1 aPetrie, M.D.1 aBrunsell, N.1 aNippert, Jesse, B. uhttps://link.springer.com/article/10.1007%2Fs00704-011-0484-y00924nas a2200133 4500008004100000245009000041210006900131300001000200490000800210520047400218100001800692700002300710856005700733 2012 eng d00aComment on "Global Resilience of Tropical Forest and Savanna to Critical Transitions"0 aComment on Global Resilience of Tropical Forest and Savanna to C a541 -0 v3363 a

Hirota et al. (Reports, 14 October 2011, p. 232) used spatial data to show that grasslands, savannas, and forests represent opposing stable states. Reanalyzing their data and drawing from temporal studies, we argue that spatial analyses underestimate the bistability of grasslands and savannas due to limitations of substituting space for time. We propose that temporal and spatial data are needed to predict critical transitions between grasslands and savannas.

1 aRatajczak, Z.1 aNippert, Jesse, B. uhttp://science.sciencemag.org/content/336/6081/541.302086nas a2200229 4500008004100000245010700041210006900148300001300217490000800230520136700238653002301605653001601628653001501644653001301659653001801672653002401690100001701714700001601731700002001747700002301767856006601790 2012 eng d00aCommunity traitscape of foliar nitrogen isotopes reveals N availabiity patterns in a tallgrass prairie0 aCommunity traitscape of foliar nitrogen isotopes reveals N avail a395 -4030 v3563 a

Background and aims Nutrients are important determinants of community assembly, yet the roles they play in structuring plant communities are still poorly understood. One inferential approach to understanding how environmental factors structure plant communities is examining the distribution of key functional traits among species of a community—a community traitscape. Methods To better understand how nitrogen (N) and water availability structure grasslands, we measured N concentrations and isotope ratios for 366 herbaceous species in a mesic N-limited temperate grassland, Konza Prairie. We also compared foliar N concentrations and N isotopes between Konza species and a global dataset. Results Species that had either high foliar N concentrations or high δ15NL were not necessarily more or less abundant on the landscape nor more or less likely to be found in uplands, grazed areas, or burned areas. Apparently there are unique hot spots of high N availability at Konza and the typical non-Fabaceae Konza species occupies sites with greater N availability than found globally. Conclusions Although nascent, the Konza traitscapes suggest that plant diversity in nutrient-limited communities might be strongly dependent on high-nutrient availability sites that enable high-fertility species to persist in a matrix of low nutrient availability.

10aCommunity assembly10adisturbance10aGrasslands10aIsotopes10aKonza Prairie10aResource limitation1 aCraine, J.M.1 aTowne, E.G.1 aOcheltree, T.W.1 aNippert, Jesse, B. uhttps://link.springer.com/article/10.1007%2Fs11104-012-1141-701990nas a2200145 4500008004100000245006300041210006300104300001300167490000700180520155400187100001801741700002301759700001901782856004301801 2012 eng d00aEcotypic responses of switchgrass to altered precipitation0 aEcotypic responses of switchgrass to altered precipitation a126 -1360 v393 a

Anthropogenic climate change is projected to alter precipitation patterns, resulting in novel environments for plants. The responses of dominant plant species (e.g. Panicum virgatum L. (switchgrass)) to climate changes can drive broader ecosystem processes such as primary productivity. Using a rainfall mesocosm facility, three ecotypes of P. virgatum (collected from Kansas, Oklahoma and Texas, USA) were subjected to three precipitation regimes (average, –25%, +25%) to determine the physiological and growth responses to altered precipitation in a common garden setting. Results showed mean maximum photosynthetic rates, stomatal conductance, transpiration, midday water potential and dark-adapted chlorophyll fluorescence were lowest in the Kansas ecotypes. Increased precipitation treatments raised the mean midday water potentials and lowered water-use efficiency. Aboveground biomass responded positively to changes in precipitation, but flowering initiation was later and rates were lower for Texas ecotypes. In general, ecotype origin was a better predictor of differences in physiological responses and flowering, whereas the precipitation treatments had greater control over biomass production. Depending on the growth variable measured, these results show responses for P. virgatum are under varying ecotypic or environmental control with few interactions, suggesting that future predictions to climate change need not inherently consider localised adaptations in this economically important and widely distributed species.

1 aHartman, J.C.1 aNippert, Jesse, B.1 aSpringer, C.J. uhttp://www.publish.csiro.au/fp/FP1122900586nas a2200121 4500008004100000245012800041210006900169260004600238490001400284100001600298700002300314856012700337 2012 eng d00aInfluences of local adaptation and genome size on Panicum virgatum (switchgrass) responses to variable precipitation timing0 aInfluences of local adaptation and genome size on Panicum virgat aPhiladelphia, PAbSt. Joseph's University0 vMS Thesis1 aO'Keefe, K.1 aNippert, Jesse, B. uhttp://knz.lternet.edu/content/influences-local-adaptation-and-genome-size-panicum-virgatum-switchgrass-responses-variable02482nas a2200229 4500008004100000245009500041210006900136300001300205490000800218520174900226653002401975653001301999653002002012653001702032653003902049653002202088100002302110700001602133700002002149700001702169856006602186 2012 eng d00aRoot characteristics of C-4 grasses limit reliance on deep soil water in tallgrass prairie0 aRoot characteristics of C4 grasses limit reliance on deep soil w a385 -3940 v3553 a

Background C4 grass species in the mesic tallgrass prairie of central North America can exhibit both high root production and deep rooting in the soil profile (>2 m). Differences in root growth and the types of roots produced vary according to local environmental gradients and management practices. The production of deep roots in tallgrass prairie has been historically presumed as a mechanism for water uptake when surface soils are dry. Methods We examined changes in root biomass, total root length, root width, and theoretical hydraulic conductivity using roots collected from deep soil cores in upland and lowland topographic positions in grazed and ungrazed watersheds of the Konza Prairie Biological Station in north-eastern Kansas, USA. Results Root biomass, total root length, and theoretical hydraulic conductivity were highest in roots found in the top 20 cm of the soil profile, and then declined exponentially with increasing soil depth. Compared to grazed areas, ungrazed locations had more root biomass and total root length of roots in the most superficial soil layers. No differences in rooting profiles were present among topographic contrasts. Theoretical hydraulic conductivity of axial root xylem did not vary by topographic position or grazing contrasts, and declines in conductivity by depth were driven by changes in the number of vessels per stele, rather than changes in vessel size. Conclusions Irrespective of differences by grazing treatment or topographic position, significant reductions in root biomass, total root length, and theoretical hydraulic conductivity of grass roots at soil depths greater than 1 m suggest deep roots in this grassland have limited functional significance for water uptake.

10aAndropogon gerardii10aC4 grass10aMesic grassland10aRoot biomass10aTheoretical hydraulic conductivity10aTotal root length1 aNippert, Jesse, B.1 aWieme, R.A.1 aOcheltree, T.W.1 aCraine, J.M. uhttps://link.springer.com/article/10.1007%2Fs11104-011-1112-401558nas a2200181 4500008004100000245006500041210006100106300001500167490000800182520099700190100001701187700002301204700001701227700001701244700002101261700001701282856007701299 2012 eng d00aThe timing of climate variability and grassland productivity0 atiming of climate variability and grassland productivity a3401 -34050 v1093 a

Changes in precipitation amount and variability have the potential to alter the structure and function of grasslands, but we know little about how changes in the timing of precipitation might affect grasslands. Here, we analyze long-term records from a tallgrass prairie to show that shifts in the timing of precipitation during the growing season have little effect on primary productivity or grass reproduction, but can greatly affect grazer performance. While greater late-season precipitation increases the weight gain of adult and young bison, greater mid-season precipitation decreases their weight gain. In addition, calving rates are lower after years with greater mid-season precipitation and higher after years with greater late-season precipitation. As well-timed drought can actually increase grazer weight gain and reproduction, it will be necessary to generate predictions of within-season distribution of precipitation to successfully forecast future grazer performance.

1 aCraine, J.M.1 aNippert, Jesse, B.1 aElmore, A.J.1 aSkibbe, A.M.1 aHutchinson, S.L.1 aBrunsell, N. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/j.1600-0706.2012.20400.x01717nas a2200145 4500008004100000245008900041210006900130300001300199490000700212520121200219100001801431700002301449700002401472856007501496 2012 eng d00aWoody encroachment decreases diversity across North American grasslands and savannas0 aWoody encroachment decreases diversity across North American gra a697 -7030 v933 a

Woody encroachment is a widespread and acute phenomenon affecting grasslands and savannas worldwide. We performed a meta-analysis of 29 studies from 13 different grassland/savanna communities in North America to determine the consequences of woody encroachment on plant species richness. In all 13 communities, species richness declined with woody plant encroachment (average decline = 45%). Species richness declined more in communities with higher precipitation (r2 = 0.81) and where encroachment was associated with a greater change in annual net primary productivity (ANPP; r2 = 0.69). Based on the strong positive correlation between precipitation and ANPP following encroachment (r2 = 0.87), we hypothesize that these relationships occur because water-limited woody plants experience a greater physiological and demographic release as precipitation increases. The observed relationship between species richness and ANPP provides support for the theoretical expectation that a trade-off occurs between richness and productivity in herbaceous communities. We conclude that woody plant encroachment leads to significant declines in species richness in North American grassland/savanna communities.

1 aRatajczak, Z.1 aNippert, Jesse, B.1 aCollins, Scott., L. uhttps://esajournals.onlinelibrary.wiley.com/doi/full/10.1890/11-1199.102524nas a2200253 4500008004100000245009600041210006900137300001500206490000800221520175800229653001701987653001902004653002202023653001502045653001802060100001702078700002302095700001602118700001502134700001702149700001702166700002102183856006602204 2011 eng d00aFunctional consequences of climate-change induced plant species loss in a tallgrass prairie0 aFunctional consequences of climatechange induced plant species l a1109 -11170 v1653 a

Future climate change is likely to reduce the floristic diversity of grasslands. Yet the potential consequences of climate-induced plant species losses for the functioning of these ecosystems are poorly understood. We investigated how climate change might alter the functional composition of grasslands for Konza Prairie, a diverse tallgrass prairie in central North America. With species-specific climate envelopes, we show that a reduction in mean annual precipitation would preferentially remove species that are more abundant in the more productive lowland positions at Konza. As such, decreases in precipitation could reduce productivity not only by reducing water availability but by also removing species that inhabit the most productive areas and respond the most to climate variability. In support of this prediction, data on species abundance at Konza over 16 years show that species that are more abundant in lowlands than uplands are preferentially reduced in years with low precipitation. Climate change is likely to also preferentially remove species from particular functional groups and clades. For example, warming is forecast to preferentially remove perennials over annuals as well as Cyperaceae species. Despite these predictions, climate change is unlikely to unilaterally alter the functional composition of the tallgrass prairie flora, as many functional traits such as physiological drought tolerance and maximum photosynthetic rates showed little relationship with climate envelope parameters. In all, although climatic drying would indirectly alter grassland productivity through species loss patterns, the insurance afforded by biodiversity to ecosystem function is likely to be sustained in the face of climate change.

10abiogeography10aClimate change10aFunctional traits10aGrasslands10aKonza Prairie1 aCraine, J.M.1 aNippert, Jesse, B.1 aTowne, E.G.1 aTucker, S.1 aKembel, S.W.1 aSkibbe, A.M.1 aMcLauchlan, K.K. uhttps://link.springer.com/article/10.1007%2Fs00442-011-1938-802693nas a2200265 4500008004100000245008500041210006900126300001500195490000800210520191600218653000902134653002002143653001902163653000802182653002002190653001502210100002302225700002002248700001702268700001702285700001402302700002802316700001702344856006602361 2011 eng d00aLinking plant growth responses across topographic gradients in tallgrass prairie0 aLinking plant growth responses across topographic gradients in t a1131 -11420 v1663 a

Aboveground biomass in grasslands varies according to landscape gradients in resource availability and seasonal patterns of growth. Using a transect spanning a topographic gradient in annually burned ungrazed tallgrass prairie, we measured changes in the height of four abundant C4 grass species, LAI, biomass, and cumulative carbon flux using two closely located eddy flux towers. We hypothesized that seasonal patterns of plant growth would be similar across the gradient, but the magnitude of growth and biomass accumulation would vary by topographic position, reflecting spatial differences in microclimate, slope, elevation, and soil depth. Thus, identifying and measuring local growth responses according to topographic variability should significantly improve landscape predictions of aboveground biomass. For most of the growth variables measured, classifying topography into four positions best captured the inherent spatial variability. Biomass produced, seasonal LAI and species height increased from the upland and break positions to the slope and lowland. Similarly, cumulative carbon flux in 2008 was greater in lowland versus upland tower locations (difference of 64 g m−2 by DOY 272). Differences in growth by topographic position reflected increased production of flowering culms by Andropogon gerardii and Sorghastrum nutans in lowland. Varying growth responses by these species may be a significant driver of biomass and carbon flux differences by topographic position, at least for wet years. Using a digital elevation model to classify the watershed into topographic positions, we performed a geographically weighted regression to predict landscape biomass. The minimum and maximum predictions of aboveground biomass for this watershed had a large range (86–393 t per 40.4 ha), illustrating the drastic spatial variability in growth within this annually-burned grassland.

10aANPP10aEddy covariance10aFlux footprint10aLAI10aMesic grassland10atopography1 aNippert, Jesse, B.1 aOcheltree, T.W.1 aSkibbe, A.M.1 aKangas, L.C.1 aHam, J.M.1 aShonkwiler-Arnold, K.B.1 aBrunsell, N. uhttps://link.springer.com/article/10.1007%2Fs00442-011-1948-602128nas a2200145 4500008004100000245008100041210006900122300000900191490000600200520164100206100001701847700001701864700002301881856007801904 2011 eng d00aPhysiological drought tolerance and the structuring of tallgrass assemblages0 aPhysiological drought tolerance and the structuring of tallgrass a48 -0 v23 a

Drought is a defining characteristic of many grasslands worldwide. Yet we have little understanding of how drought structures grassland communities and the degree to which physiological drought tolerance advantages plants in grasslands. We characterized physiological drought tolerance (Ψcrit) for a large number of species in a mesic grassland community (Konza Prairie, KS, USA). We then examined the relationships between Ψcrit and a number of other key functional traits, and tested whether physiological tolerance of drought underlay success across a number of ecological contrasts—topographic position, burn frequency, and grazing—with 17 years of abundance data. Physiological drought tolerance of Konza species covered almost the full range known to plants globally. Consistently, physiologically drought-tolerant species had thin roots, while associations with other traits were inconsistent across functional groups. In this mesic grassland, physiological drought tolerance appears to increase the abundance of plants in xeric uplands, but does not in the mesic lowlands. Physiological drought tolerance did not alter species responses to changes in burning or grazing. In contrast to Ψcrit, species with high root tissue density were more abundant in uplands and lowlands than species with low root tissue density largely irrespective of grazing or burning regimes. In all, drought appears to have a limited role in structuring the Konza plant community. As such, more severe or frequent droughts in the region would likely restructure the Konza plant community in ways that are currently not observable.

1 aTucker, S.S.1 aCraine, J.M.1 aNippert, Jesse, B. uhttps://esajournals.onlinelibrary.wiley.com/doi/full/10.1890/ES11-00023.102412nas a2200157 4500008004100000245008600041210006900127300001000196490000600206520188500212100001802097700002302115700001802138700002002156856007802176 2011 eng d00aPositive feedbacks amplify rates of woody encroachment in mesic tallgrass prairie0 aPositive feedbacks amplify rates of woody encroachment in mesic  a121 -0 v23 a

Over the last century, many grasslands worldwide have transitioned from a graminoid to a tree/shrub-dominated state in a short period of time, a phenomenon referred to as woody encroachment. Positive feedbacks and bi-stability are thought to be important drivers of woody encroachment, but there is little empirical evidence to suggest that positive feedbacks accelerate the woody encroachment of mesic grasslands. In mesic tallgrass prairie, shrub establishment does not directly facilitate seedling establishment. Yet, shrub establishment may facilitate the clonal spread of existing shrubs into nearby patches, because clonal reproduction might circumvent barriers that typically limit woody seedlings. Our results show that when Cornus drummondii (the predominate encroacher of mesic tallgrass prairie) extends rhizomatous stems into open grasslands, these stems use the same deep soil water sources as mature stems—thereby avoiding competition with grasses and gaining access to a reliable water source. In addition, herbaceous fuel concentrations are lower at the shrub/grass interface than in open grasslands, reducing the potential impacts of subsequent grassland fires. We propose that the release from resource and fire limitation results in a positive feedback loop as clonal stems are able to extend into surrounding patches, circumvent demographic barriers, mature, and spread by developing their own clonal stems. Long-term data on site (26 years) corroborates this interpretation: the size of deep-rooted clonal shrub species has increased 16-fold and their cover has increased from 0 to 27%, whereas the cover of shallow-rooted species (both clonal and non-clonal) has only increased marginally. Together, these results suggest that (1) positive feedbacks can facilitate mesic woody encroachment and (2) bi-stability exists in mesic tallgrass prairie.

1 aRatajczak, Z.1 aNippert, Jesse, B.1 aHartman, J.C.1 aOcheltree, T.W. uhttps://esajournals.onlinelibrary.wiley.com/doi/full/10.1890/ES11-00212.102001nas a2200229 4500008004100000245012300041210006900164300001500233490000700248520124600255653002501501653001801526653001301544653002801557653001801585653000801603100001801611700002301629700001701652700001901669856008301688 2011 eng d00aPotential ecological impacts of switchgrass (Panicum virgatum L.) biofuel cultivation in the Central Great Plains, USA0 aPotential ecological impacts of switchgrass Panicum virgatum L b a3415 -34210 v353 a

Switchgrass (Panicum virgatum L.) is a broadly adapted warm-season grass species native to most of the central and eastern United States. Switchgrass has been identified as a potential biofuel species because it is a native species that requires minimal management, and has a large potential to sequester carbon underground. Since the 1990’s, switchgrass has been bred to produce cultivars with increased biomass and feedstock quality. This review addresses potential ecological consequences of widespread switchgrass cultivation for biofuel production in the central United States. Specifically, this review address the ecological implications of changing use of marginal and CRP land, impacts on wildlife, potentials for disease and invasions, and changes in soil quality through reductions in erosion, decomposition rates, and carbon sequestrations. A central theme of the review is the utility of maintaining landscape heterogeneity during switchgrass biofuel production. This includes implementing harvest rotations, no till farming, and mixed species composition. If negative ecological consequences of switchgrass cultivation are minimized, biofuel production using this species has economical and environmental benefits.

10aCarbon sequestration10aCrop rotation10aCRP land10aLandscape heterogeneity10aMarginal land10aSOC1 aHartman, J.C.1 aNippert, Jesse, B.1 aOrozco, R.A.1 aSpringer, C.J. uhttps://www.sciencedirect.com/science/article/pii/S0961953411002935?via%3Dihub02899nas 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/8/3053/2011/03241nas a2200193 4500008004100000245009100041210006900132260004300201490001400244520262400258653002402882653001202906653001902918653001802937653001402955100001802969700002302987856003703010 2011 eng d00aResponses of switchgrass (Panicum virgatum L.) to precipitation amount and temperature0 aResponses of switchgrass Panicum virgatum L to precipitation amo aManhattan, KSbKansas State University0 vMS Thesis3 a

Anthropogenic climate change is likely to alter the function and composition of ecosystems worldwide through increased precipitation variability and temperatures. To predict ecosystem responses, a greater understanding of the physiological and growth responses of plants is required. Dominant species drive ecosystem responses, and it is essential to understand how they respond to understand potential ecosystem changes. Dominant species, such as switchgrass (Panicum virgatum L.), posses large genotypic and phenotypic variability, which will impact the degree of responses to projected climate changes. I studied the physiological and growth responses of switchgrass, a common perennial warm-season C4 grass that is native to the tallgrass prairie, to alterations in precipitation amount and temperature. The first experiment I conducted focused on the responses of three ecotypes of P. virgatum to three precipitation regimes (average, 25% below, 25% above). I concluded that the physiological responses of photosynthesis, stomatal conductance, transpiration, dark-adapted fluorescence, and mid-day water potential in P. virgatum were explained by ecotypic differences. Robust responses to altered precipitation were seen in the water use efficiency, mid-day water potential, and aboveground biomass. Ecotypic differences were also seen in several aboveground biomass variables, and most strikingly in flowering times and rates. There were few interactions between ecotype and precipitation, suggesting precipitation is a strong driver of biomass production, whereas adaption of ecotypes to their local environment affects physiological processes. A second experiment studied the response of local populations of P. virgatum to nocturnal warming. Results showed significant differences in daytime E, daytime gs, and flowering phenology between treatments. Differences in aboveground biomass were between topographic positions. I concluded that water availability, based on topographic position, is a strong driver of P. virgatum aboveground biomass production, but nocturnal warming has the potential to impact flowering phenology, physiological responses, and exacerbate plant water stress. I also reviewed the literature on the ecological effects of implementing switchgrass cultivation for biofuel. From the literature review, I concluded that large-scale switchgrass cultivation will have widespread ecological impacts. If landscape heterogeneity is maintained through harvest rotations, no till farming, and mixed species composition, ecosystem services can be maintained while providing economic value.

10aAboveground biomass10aBiofuel10aClimate change10aEcophysiology10agrassland1 aHartman, J.C.1 aNippert, Jesse, B. uhttp://hdl.handle.net/2097/1072002131nas a2200145 4500008004100000245009200041210006900133300001500202490000700217520163100224100001701855700001601872700002301888856007401911 2010 eng d00aClimate controls on grass culm production over a quarter century in a tallgrass prairie0 aClimate controls on grass culm production over a quarter century a2132 -21400 v913 a

The flowering of grasses is a process critical to plant population dynamics and genetics, herbivore performance, and human health. To better understand the climate factors governing grass flowering, we analyzed the patterns of culm production over 25 years for three perennial tallgrass prairie species at Konza Prairie in Kansas, USA. The three species (Andropogon gerardii, Sorghastrum nutans, and Schizachyrium scoparium) all utilize the C4 photosynthetic pathway and were measured annually at the same locations for the past 25 years in an annually burned watershed. Culm production of all three species increased with higher growing-season soil moisture and precipitation but differed in their responses to water availability at different times during the growing season. Relative to Andropogon, Sorghastrum responded more to precipitation early in the growing season, and Schizachyrium responded more to precipitation late in the growing season. Flowering by each species also revealed a threshold relationship with late-season soil moisture at ~1 m depth, which likely is a proxy for season-long water balance. Although flowering can be influenced by conditions antecedent to the current growing season, neither soil moisture nor precipitation during the previous year influenced flowering over the 25-year period. Flowering culm production averaged 9% and 7% of total graminoid aboveground net primary production (ANPP) in the uplands and lowlands, respectively. Interannual variation in ANPP correlated only with Sorghastrum flowering, suggesting a predominant role of the species in ANPP responses to climate.

1 aCraine, J.M.1 aTowne, E.G.1 aNippert, Jesse, B. uhttps://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/09-1242.103017nas a2200181 4500008004100000245010600041210006900147260004300216490001400259520239000273653002102663653002202684653001702706653002202723100001502745700002302760856005202783 2010 eng d00aMorphological and physiological traits as indicators of drought tolerance in tallgrass prairie plants0 aMorphological and physiological traits as indicators of drought  aManhattan, KSbKansas State University0 vMS Thesis3 a

The Konza Prairie in northern Kansas, USA contains over 550 vascular plant species; of which, few have been closely studied. These species are adapted to environmental stress as imposed by variable temperature, precipitation, fire, and grazing. Understanding which plant traits relate to drought responses will allow us to both predict drought tolerance and potential future shifts in plant community composition from changes in local climate. Morphological and physiological measurements were taken on 121 species of herbaceous tallgrass prairie plants grown from seed in a growth chamber. Gas exchange measurements including maximum photosynthetic rate, stomatal conductance to water vapor, and intercellular CO[subscript]2 concentration were measured. All plants were exposed to a drought treatment and were monitored daily until stomatal conductance was zero. At this point, critical leaf water potential (Ψ[subscript]crit), an indicator of physiological drought tolerance was assessed. Other measurements include root length, diameter, volume, and mass, leaf area, leaf tissue density, root tissue density, and root to shoot ratio. Traits were compared using pair-wise bivariate analysis and principal component analysis (PCA). A dichotomy was found between dry-adapted plants with thin, dense leaves and roots, high leaf angle, and highly negative Ψ[subscript]crit and hydrophiles which have the opposite profile. A second axis offers more separation based on high photosynthetic rate, high conductance rate, and leaf angle, but fails to provide a distinction between C[subscript]3 and C[subscript]4 species. When tested independently, grasses and forbs both showed drought tolerance strategies similar to the primary analysis. Matching up these axes with long term abundance data suggests that species with drought tolerance traits have increased abundance on Konza, especially in upland habitats. However, traits that relate to drought tolerance mirror relationships with nutrient stress, confounding separation of low water versus low nutrient strategies. My results not only illustrate the utility of morphological and physiological plant traits in classifying drought responses across a range of species, but as functional traits in predicting both drought tolerance in individual species and relative abundance across environmental gradients of water availability.

10aAbundance; Konza10aDrought Tolerance10aPlant traits10atallgrass prairie1 aTucker, S.1 aNippert, Jesse, B. uhttp://krex.k-state.edu/dspace/handle/2097/462802253nas 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.x02307nas 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%3Dihub02594nas a2200169 4500008004100000245012200041210006900163300001500232490000700247520200200254100001402256700001802270700002302288700001902311700001702330856007702347 2008 eng d00aChanges in grassland ecosystem function due to extreme rainfall events: implications for responses to climate change0 aChanges in grassland ecosystem function due to extreme rainfall  a1600 -16080 v143 a

Climate change is causing measurable changes in rainfall patterns, and will likely cause increases in extreme rainfall events, with uncertain implications for key processes in ecosystem function and carbon cycling. We examined how variation in rainfall total quantity (Q), the interval between rainfall events (I), and individual event size (SE) affected soil water content (SWC) and three aspects of ecosystem function: leaf photosynthetic carbon gain (inline image), aboveground net primary productivity (ANPP), and soil respiration (inline image). We utilized rainout shelter-covered mesocosms (2.6 m3) containing assemblages of tallgrass prairie grasses and forbs. These were hand watered with 16 I×Q treatment combinations, using event sizes from 4 to 53 mm. Increasing Q by 250% (400–1000 mm yr−1) increased mean soil moisture and all three processes as expected, but only by 20–55% (P≤0.004), suggesting diminishing returns in ecosystem function as Q increased. Increasing I (from 3 to 15 days between rainfall inputs) caused both positive (inline image) and negative (inline image) changes in ecosystem processes (20–70%, P≤0.01), within and across levels of Q, indicating that I strongly influenced the effects of Q, and shifted the system towards increased net carbon uptake. Variation in SE at shorter I produced greater response in soil moisture and ecosystem processes than did variation in SE at longer I, suggesting greater stability in ecosystem function at longer I and a priming effect at shorter I. Significant differences in ANPP and inline image between treatments differing in I and Q but sharing the same SE showed that the prevailing pattern of rainfall influenced the responses to a given event size. Grassland ecosystem responses to extreme rainfall patterns expected with climate change are, therefore, likely to be variable, depending on how I, Q, and SE combine, but will likely result in changes in ecosystem carbon cycling.

1 aFay, P.A.1 aKaufman, D.M.1 aNippert, Jesse, B.1 aCarlisle, J.D.1 aHarper, C.W. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2486.2008.01605.x02334nas a2200193 4500008004100000245006800041210006800109300001300177490000800190520170900198653001401907653001401921653001701935653003201952653002201984100002302006700002002029856009102049 2007 eng d00aLinking water uptake with rooting patterns in grassland species0 aLinking water uptake with rooting patterns in grassland species a261 -2720 v1533 aWater availability strongly governs grassland primary productivity, yet this resource varies dramatically in time (seasonally) and space (with soil depth and topography). It has long been assumed that co-occurring species differ in their partitioning of water use by depth, but direct evidence is lacking. We report data from two growing seasons (2004–2005) in which we measured the isotopic signature of plant xylem water from seven species (including C3 forbs and shrubs and C4 grasses) growing along a topographic gradient at the Konza Prairie Biological Station. Plant xylem stable oxygen isotope ratio (δ18O) values were compared to soil water δ18O profiles, recent rainfall events, and groundwater. Species varied in both their temporal patterns of water use and their responses to seasonal droughts in both years. During wet periods, species differences in water use were minimal, with common dependency on recent rainfall events stored in the upper soil layers. However, during dry periods, most C3 species used proportionally more water from deeper portions of the soil profile relative to the C4 grasses. Plants in uplands used more shallow soil water compared to those in lowlands, with the greatest differences across the topographic gradient occurring during dry periods. While the documented vertical root distribution varies by species and growth form in this grassland, each of the species we measured appeared to compete for the same surface layer soil moisture when water was not limiting. Thus, our results suggest that variation in precipitation history and landscape positions are greater determinants of water-use patterns than would be expected based on absolute rooting depth.10aC3 plants10aC4 plants10aMixing model10aStable oxygen isotope ratio10atallgrass prairie1 aNippert, Jesse, B.1 aKnapp, Alan, K. uhttp://knz.lternet.edu/content/linking-water-uptake-rooting-patterns-grassland-species01970nas a2200229 4500008004100000245009200041210006900133300001300202490000700215520123600222653001601458653000701474653000701481653002901488653001701517653001001534653002201544100002301566700001401589700002001603856011701623 2007 eng d00aPhotosynthetic traits in C3 and C4 grassland species in mesocosm and field environments0 aPhotosynthetic traits in C3 and C4 grassland species in mesocosm a412 -4200 v603 aThe North American tallgrass prairie is composed of a diverse mix of C3 and C4 plant species that are subject to multiple resource limitations. C4 grasses dominate this ecosystem, purportedly due to greater photosynthetic capacity and resource-use efficiency associated with C4 photosynthesis. We tested the hypothesis that intrinsic physiological differences between C3 and C4 species are consistent with C4 grass dominance by comparing leaf gas exchange and chlorophyll fluorescence variables for seven C4 and C3 herbaceous species (legumes and non-legumes) in two different settings: experimental mesocosms and natural grassland sites. In the mesocosms, C4 grasses had higher photosynthetic rates, water potentials and water-use efficiency than the C3 species. These differences were absent in the field, where photosynthetic rates declined similarly among non-leguminous species. Thus, intrinsic photosynthetic advantages for C4 species measured in resource-rich mesocosms could not explain the dominance of C4 species in the field. Instead, C4 dominance in this ecosystem may depend more on the ability of the grasses to grow rapidly when resources are plentiful and to tolerate multiple limitations when resources are scarce.10aA:Ci curves10aC310aC410aChlorophyll fluorescence10agas exchange10aKonza10atallgrass prairie1 aNippert, Jesse, B.1 aFay, P.A.1 aKnapp, Alan, K. uhttp://knz.lternet.edu/content/photosynthetic-traits-c3-and-c4-grassland-species-mesocosm-and-field-environments02388nas a2200133 4500008004100000245008400041210006900125300001500194490000800209520188500217100002302102700002002125856010902145 2007 eng d00aSoil water partitioning contributes to species coexistence in tallgrass prairie0 aSoil water partitioning contributes to species coexistence in ta a1017 -10290 v1163 aThe majority of tallgrass prairie root biomass is located in the upper soil layers (0–25 cm), but species differences exist in reliance on soil water at varying depths. These differences have led to the hypothesis that resource partitioning belowground facilitates species co-existence in this mesic grassland. To determine if plant water relations can be linked to soil water partitioning as a potential mechanism allowing C3 species to persist among the more dominant C4 grasses, we measured differences in the source of water-use using the isotopic signature of xylem water, volumetric soil water content at 4 depths, and leaf water potentials. Data were collected for seven species representing C4 grasses, C3 forbs and C3 shrubs over three growing seasons at the Konza Prairie (Kansas, USA) to encompass a range of natural climatic conditions. C4 grasses relied on shallow soil water (5 cm) across the growing season and had midday leaf water potentials that were highly correlated with shallow soil water regardless of soil water availability at other portions of the soil profile (20, 40 and 90 cm). In contrast, C3 species only used shallow soil water when plentiful at this depth; these species increased their dependence on soil water from greater depths as the upper soil layers dried. Structural equation models describing plant water relations were very similar for the three C4 species, whereas a unique set of models and drivers were identified for each of the C3 species. These results support soil water partitioning as a mechanism for species coexistence, as C4 species in this grassland have relatively consistent dependence on water in shallow soil layers, whereas C3 species show niche differentiation in water use strategies to avoid competition with C4 grasses for water in shallow soil layers when this resource is limiting and leaf water stress is high.1 aNippert, Jesse, B.1 aKnapp, Alan, K. uhttp://knz.lternet.edu/content/soil-water-partitioning-contributes-species-coexistence-tallgrass-prairie02991nas a2200217 4500008004100000245009600041210006900137300001100206490000800217520225200225653000902477653001902486653001402505653003002519653001802549653002202567100002302589700002002612700001902632856012202651 2006 eng d00aIntra-annual rainfallvariability and grassland productivity: can the past predictthe future0 aIntraannual rainfallvariability and grassland productivity can t a65 -740 v1843 aPrecipitation quantity has been shown to influence grassland aboveground net primary productivity (ANPP) positively whereas experimental increases in of temporal variability in water availability commonly exhibit a negative relationship with ANPP. We evaluated long term ANPP datasets from the Konza Prairie Long Term Ecological Research (LTER) program (1984–1999) to determine if similar relationships could be identified based on patterns of natural variability (magnitude and timing) in precipitation. ANPP data were analyzed from annually burned sites in native mesic grassland and productivity was partitioned into graminoid (principally C4 grasses) and forb (C3 herbaceous) components. Although growing season precipitation amount was the best single predictor of total and grass ANPP (r 2=0.62), several measures of precipitation variability were also significantly and positively correlated with productivity, independent of precipitation amount. These included soil moisture variability, expressed as CV, for June (r 2=0.45) and the mean change in soil moisture between weekly sampling periods in June and August (%wv) (r 2=0.27 and 0.32). In contrast, no significant relationships were found between forb productivity and any of the precipitation variables (p>0.05). A multiple regression model combining precipitation amount and both measures of soil moisture variability substantially increased the fit with productivity (r 2=0.82). These results were not entirely consistent with those of short-term manipulative experiments in the same grassland, however, because soil moisture variability was often positively, not negatively related to ANPP. Differences in results between long and short term experiments may be due to low variability in the historic precipitation record compared to that imposed experimentally as experimental levels of variability exceeded the natural variability of this dataset by a factor of two. Thus, forecasts of ecosystem responses to climate change (i.e. increased climatic variability), based on data constrained by natural and recent historical rainfall patterns may be inadequate for assessing climate change scenarios if precipitation variability in the future is expected to exceed current levels.10aANPP10aClimate change10agrassland10aPrecipitation variability10asoil moisture10atallgrass prairie1 aNippert, Jesse, B.1 aKnapp, Alan, K.1 aBriggs, J., M. uhttp://knz.lternet.edu/content/intra-annual-rainfallvariability-and-grassland-productivity-can-past-predictthe-future00499nas a2200121 4500008004100000245009500041210006900136260004800205300001100253490002100264100002300285856006900308 2006 eng d00aLife by the drop: Water as a physiological driver of the tallgrass prairie plant community0 aLife by the drop Water as a physiological driver of the tallgras aFort Collins, CObColorado State University a1 -1480 vPhD Dissertation1 aNippert, Jesse, B. uhttps://search.proquest.com/docview/305354527/?pq-origsite=primo00453nas a2200109 4500008004100000245011400041210006900155490000600224100002300230700002000253856007000273 2005 eng d00aComparing the influence of precipitation, fire, and topography on plant productivity in the tallgrass prairie0 aComparing the influence of precipitation fire and topography on 0 v31 aNippert, Jesse, B.1 aBlair, John, M. uhttp://tiee.ecoed.net/vol/v3/issues/data_sets/konza/abstract.html03031nas a2200349 4500008004100000245009100041210006900132300001100201490000800212520198400220653001202204653003002216653002602246653001502272653001202287100001702299700001702316700001502333700001402348700002102362700002002383700002002403700001702423700001902440700001802459700002302477700001602500700001702516700001702533700001502550856011602565 2004 eng d00aWater relations in grassland and desert ecosystems exposed to elevated atmospheric CO20 aWater relations in grassland and desert ecosystems exposed to el a11 -250 v1403 a

Atmospheric CO2 enrichment may stimulate plant growth directly through (1) enhanced photosynthesis or indirectly, through (2) reduced plant water consumption and hence slower soil moisture depletion, or the combination of both. Herein we describe gas exchange, plant biomass and species responses of five native or semi-native temperate and Mediterranean grasslands and three semi-arid systems to CO2 enrichment, with an emphasis on water relations. Increasing CO2 led to decreased leaf conductance for water vapor, improved plant water status, altered seasonal evapotranspiration dynamics, and in most cases, periodic increases in soil water content. The extent, timing and duration of these responses varied among ecosystems, species and years. Across the grasslands of the Kansas tallgrass prairie, Colorado shortgrass steppe and Swiss calcareous grassland, increases in aboveground biomass from CO2 enrichment were relatively greater in dry years. In contrast, CO2-induced aboveground biomass increases in the Texas C3/C4 grassland and the New Zealand pasture seemed little or only marginally influenced by yearly variation in soil water, while plant growth in the Mojave Desert was stimulated by CO2 in a relatively wet year. Mediterranean grasslands sometimes failed to respond to CO2-related increased late-season water, whereas semiarid Negev grassland assemblages profited. Vegetative and reproductive responses to CO2 were highly varied among species and ecosystems, and did not generally follow any predictable pattern in regard to functional groups. Results suggest that the indirect effects of CO2 on plant and soil water relations may contribute substantially to experimentally induced CO2-effects, and also reflect local humidity conditions. For landscape scale predictions, this analysis calls for a clear distinction between biomass responses due to direct CO2 effects on photosynthesis and those indirect CO2 effects via soil moisture as documented here.

10abiomass10aCarbon dioxide enrichment10aLandscape predictions10asoil water10aStomata1 aMorgan, J.A.1 aPataki, D.E.1 aKorner, C.1 aClark, H.1 aDel Grosso, S.J.1 aGrunzweig, J.M.1 aKnapp, Alan, K.1 aMosier, A.R.1 aNewton, P.C.D.1 aNiklaus, P.A.1 aNippert, Jesse, B.1 aNowak, R.S.1 aParton, W.J.1 aPolley, H.W.1 aShaw, M.R. uhttp://knz.lternet.edu/content/water-relations-grassland-and-desert-ecosystems-exposed-elevated-atmospheric-co2