02899nas 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/8/3053/2011/02307nas 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.x03504nas a2200169 4500008004100000245011200041210006900153300001300222490000700235520287400242100001703116700002003133700001403153700002003167700001903187856012803206 2005 eng d00aIncreased rainfall variability and reduced rainfall amount decreases soil CO2 flux in a grassland ecosystem0 aIncreased rainfall variability and reduced rainfall amount decre a322 -3440 v113 aPredicted climate changes in the US Central Plains include altered precipitation regimes with increased occurrence of growing season droughts and higher frequencies of extreme rainfall events. Changes in the amounts and timing of rainfall events will likely affect ecosystem processes, including those that control C cycling and storage. Soil carbon dioxide (CO2) flux is an important component of C cycling in terrestrial ecosystems, and is strongly influenced by climate. While many studies have assessed the influence of soil water content on soil CO2 flux, few have included experimental manipulation of rainfall amounts in intact ecosystems, and we know of no studies that have explicitly addressed the influence of the timing of rainfall events. In order to determine the responses of soil CO2 flux to altered rainfall timing and amounts, we manipulated rainfall inputs to plots of native tallgrass prairie (Konza Prairie, Kansas, USA) over four growing seasons (1998–2001). Specifically, we altered the amounts and/or timing of growing season rainfall in a factorial combination that included two levels of rainfall amount (100% or 70% of naturally occurring rainfall quantity) and two temporal patterns of rain events (ambient timing or a 50% increase in length of dry intervals between events). The size of individual rain events in the altered timing treatment was adjusted so that the quantity of total growing season rainfall in the ambient and altered timing treatments was the same (i.e. fewer, but larger rainfall events characterized the altered timing treatment). Seasonal mean soil CO2 flux decreased by 8% under reduced rainfall amounts, by 13% under altered rainfall timing, and by 20% when both were combined (P<0.01). These changes in soil CO2 flux were consistent with observed changes in plant productivity, which was also reduced by both reduced rainfall quantity and altered rainfall timing. Soil CO2 flux was related to both soil temperature and soil water content in regression analyses; together they explained as much as 64% of the variability in CO2 flux across dates under ambient rainfall timing, but only 38–48% of the variability under altered rainfall timing, suggesting that other factors (e.g. substrate availability, plant or microbial stress) may limit CO2 flux under a climate regime that includes fewer, larger rainfall events. An analysis of the temperature sensitivity of soil CO2 flux indicated that temperature had a reduced effect (lower correlation and lower Q10 values) under the reduced quantity and altered timing treatments. Recognition that changes in the timing of rainfall events may be as, or more, important than changes in rainfall amount in affecting soil CO2 flux and other components of the carbon cycle highlights the complex nature of ecosystem responses to climate change in North American grasslands.1 aHarper, C.W.1 aBlair, John, M.1 aFay, P.A.1 aKnapp, Alan, K.1 aCarlisle, J.D. uhttp://knz.lternet.edu/content/increased-rainfall-variability-and-reduced-rainfall-amount-decreases-soil-co2-flux-grassland02608nas a2200229 4500008004100000245008400041210006900125300001300194490000800207520185900215653001902074653001802093653002902111653001802140653001802158100001202176700001902188700002002207700002002227700002402247856010702271 2003 eng d00aProductivity responses to altered rainfall patterns in a C4-dominated grassland0 aProductivity responses to altered rainfall patterns in a C4domin a245 -2510 v1373 aRainfall variability is a key driver of ecosystem structure and function in grasslands worldwide. Changes in rainfall patterns predicted by global climate models for the central United States are expected to cause lower and increasingly variable soil water availability, which may impact net primary production and plant species composition in native Great Plains grasslands. We experimentally altered the timing and quantity of growing season rainfall inputs by lengthening inter-rainfall dry intervals by 50%, reducing rainfall quantities by 30%, or both, compared to the ambient rainfall regime in a native tallgrass prairie ecosystem in northeastern Kansas. Over three growing seasons, increased rainfall variability caused by altered rainfall timing with no change in total rainfall quantity led to lower and more variable soil water content (0–30 cm depth), a ~10% reduction in aboveground net primary productivity (ANPP), increased root to shoot ratios, and greater canopy photon flux density at 30 cm above the soil surface. Lower total ANPP primarily resulted from reduced growth, biomass and flowering of subdominant warm-season C4 grasses while productivity of the dominant C4 grass Andropogon gerardii was relatively unresponsive. In general, vegetation responses to increased soil water content variability were at least equal to those caused by imposing a 30% reduction in rainfall quantity without altering the timing of rainfall inputs. Reduced ANPP most likely resulted from direct effects of soil moisture deficits on root activity, plant water status, and photosynthesis. Altered rainfall regimes are likely to be an important element of climate change scenarios in this grassland, and the nature of interactions with other climate change elements remains a significant challenge for predicting ecosystem responses to climate change.10aClimate change10aKonza Prairie10aNet primary productivity10aPrecipitation10asoil moisture1 aFay, P.1 aCarlisle, J.D.1 aKnapp, Alan, K.1 aBlair, John, M.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/productivity-responses-altered-rainfall-patterns-c4-dominated-grassland00772nas a2200205 4500008004100000245010400041210006900145260004400214300001300258653002200271100001200293700002000305700002000325700001900345700001700364700001900381700001800400700002000418856012800438 2003 eng d00aRainfall timing, soil moisture dynamics, and plant responses in a mesic tallgrass prairie ecosystem0 aRainfall timing soil moisture dynamics and plant responses in a  aTucson, AZbUniversity of Arizona Press a147 -16310atallgrass prairie1 aFay, P.1 aKnapp, Alan, K.1 aBlair, John, M.1 aCarlisle, J.D.1 aDanner, B.T.1 aMcCarron, J.K.1 aWeltzin, J.F.1 aMcPherson, G.R. uhttp://knz.lternet.edu/content/rainfall-timing-soil-moisture-dynamics-and-plant-responses-mesic-tallgrass-prairie-ecosystem00700nas a2200205 4500008004100000245008600041210006900127300001300196490000800209100001400217700001900231700001700250700001500267700001900282700001600301700002000317700002000337700002400357856011300381 2002 eng d00aAltered rainfall patterns, gas exchange and growth in C3 and C4 grassland species0 aAltered rainfall patterns gas exchange and growth in C3 and C4 g a549 -5570 v1631 aFay, P.A.1 aCarlisle, J.D.1 aDanner, B.T.1 aLett, M.S.1 aMcCarron, J.K.1 aStewart, C.1 aKnapp, Alan, K.1 aBlair, John, M.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/altered-rainfall-patterns-gas-exchange-and-growth-c3-and-c4-grassland-species01540nas a2200229 4500008004100000245009000041210006900131300001500200490000800215520084900223100002001072700001401092700002001106700002401126700001601150700001901166700001701185700001701202700001501219700001901234856005701253 2002 eng d00aRainfall variability, carbon cycling and plant species diversity in a mesic grassland0 aRainfall variability carbon cycling and plant species diversity  a2202 -22050 v2983 a

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

1 aKnapp, Alan, K.1 aFay, P.A.1 aBlair, John, M.1 aCollins, Scott., L.1 aSmith, M.D.1 aCarlisle, J.D.1 aHarper, C.W.1 aDanner, B.T.1 aLett, M.S.1 aMcCarron, J.K. uhttps://science.sciencemag.org/content/298/5601/220202614nas a2200277 4500008004100000245008000041210006900121300001300190490000700203520177300210653001201983653001701995653002102012653001202033653002202045100001402067700001902081700001702100700001502117700001902132700001602151700002002167700002002187700002402207856010502231 2001 eng d00aCarbon and water relations of juvenile Quercus species in tallgrass prairie0 aCarbon and water relations of juvenile Quercus species in tallgr a807 -8160 v123 aIn ecosystems where environments are extreme, such as deserts, adult plant species may facilitate the establishment and growth of seedlings and juveniles. Because high temperatures and evaporative demand characterize tall-grass prairies of the central United States (relative to forests), we predicted that the grassland-forest ecotone, by minimizing temperature extremes and moderating water stress, may function to facilitate the expansion of Quercus species into undisturbed tall-grass prairie. We assessed the carbon and water relations of juvenile Quercus macrocarpa and Q. muhlenbergii, the dominant tree species in gallery forests of northeast Kansas, in ecotone and prairie sites. To evaluate the potentially competitive effects of neighboring herbaceous biomass on these oaks, juveniles (< 0.5 m tall) of both species also were subjected to either: (1) removal of surrounding above-ground herbaceous biomass, or (2) control (prairie community intact) treatments. Herbaceous biomass removal had no significant effect on gas exchange or water relations in these oak species in either the prairie or the ecotone environment. Although the ecotone did alleviate some environmental extremes, photosynthetic rates and stomatal conductance were ca. 20 % higher (p < 0.05) in both oaks in prairie sites vs. the ecotone. Moreover, although leaf temperatures on average were higher in oaks in the prairie, high leaf temperatures in the ecotone had a greater negative effect on photosynthesis. These data suggest that the grassland-forest ecotone did not facilitate the growth of Quercus juveniles expanding into this grassland. Moreover, the carbon and water relations of juvenile oaks in the prairie appeared to be unaffected by the presence of the dominant C4 grasses.10aEcotone10aFacilitation10aforest expansion10aQuercus10atallgrass prairie1 aFay, P.A.1 aCarlisle, J.D.1 aDanner, B.T.1 aLett, M.S.1 aMcCarron, J.K.1 aStewart, C.1 aKnapp, Alan, K.1 aBlair, John, M.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/carbon-and-water-relations-juvenile-quercus-species-tallgrass-prairie02886nas a2200289 4500008004100000245013100041210006900172300001300241490000600254520190600260653001902166653002402185653001502209653001802224653001902242653002302261653002702284653002702311653002102338653001802359100001402377700001902391700002002410700002002430700002402450856012202474 2000 eng d00aAltering rainfall timing and quantity in a mesic grassland ecosystem: Design and performance of rainfall manipulation shelters0 aAltering rainfall timing and quantity in a mesic grassland ecosy a308 -3190 v33 aGlobal climate change is predicted to alter growing season rainfall patterns, potentially reducing total amounts of growing season precipitation and redistributing rainfall into fewer but larger individual events. Such changes may affect numerous soil, plant, and ecosystem properties in grasslands and ultimately impact their productivity and biological diversity. Rainout shelters are useful tools for experimental manipulations of rainfall patterns, and permanent fixed-location shelters were established in 1997 to conduct the Rainfall Manipulation Plot study in a mesic tallgrass prairie ecosystem in northeastern Kansas. Twelve 9 x 14–m fixed-location rainfall manipulation shelters were constructed to impose factorial combinations of 30% reduced rainfall quantity and 50% greater interrainfall dry periods on 6 x 6–m plots, to examine how altered rainfall regimes may affect plant species composition, nutrient cycling, and above- and belowground plant growth dynamics. The shelters provided complete control of growing season rainfall patterns, whereas effects on photosynthetic photon flux density, nighttime net radiation, and soil temperature generally were comparable to other similar shelter designs. Soil and plant responses to the first growing season of rainfall manipulations (1998) suggested that the interval between rainfall events may be a primary driver in grassland ecosystem responses to altered rainfall patterns. Aboveground net primary productivity, soil CO2 flux, and flowering duration were reduced by the increased interrainfall intervals and were mostly unaffected by reduced rainfall quantity. The timing of rainfall events and resulting temporal patterns of soil moisture relative to critical times for microbial activity, biomass accumulation, plant life histories, and other ecological properties may regulate longer-term responses to altered rainfall patterns.10aClimate change10afloristic diversity10aGrasslands10aKonza Prairie10alife histories10along-term research10aNet primary production10aprecipitation patterns10arainout shelters10asoil moisture1 aFay, P.A.1 aCarlisle, J.D.1 aKnapp, Alan, K.1 aBlair, John, M.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/altering-rainfall-timing-and-quantity-mesic-grassland-ecosystem-design-and-performance