00749nas a2200193 4500008004500000245013100045210006900176100002000245700002500265700002500290700002600315700003000341700002700371700001800398700002200416700002300438700001800461856007600479 In Press eng d 00aField experiments have enhanced our understanding of drought impacts on terrestrial ecosystems—But where do we go from here?0 aField experiments have enhanced our understanding of drought imp1 aKnapp, Alan, K.1 aCondon, Kathleen, V.1 aFolks, Christine, C.1 aSturchio, Matthew, A.1 aGriffin-Nolan, Robert, J.1 aKannenberg, Steven, A.1 aGill, Amy, S.1 aHajek, Olivia, L.1 aSiggers, Alexander1 aSmith, M., D. uhttps://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2435.1446000853nas a2200265 4500008004500000245010900045210006900154100001400223700003000237700002500267700001600292700001300308700001400321700002500335700002100360700001400381700001800395700001600413700001900429700002000448700001700468700001700485700001600502856006900518 In Press eng d 00aGrassland sensitivity to drought is related to functional composition across East Asia and North America0 aGrassland sensitivity to drought is related to functional compos1 aSong, Lin1 aGriffin-Nolan, Robert, J.1 aMuraina, Taofeek, O.1 aChen, Jiaqi1 aTe, Niwu1 aShi, Yuan1 aWhitney, Kenneth, D.1 aZhang, Bingchuan1 aYu, Qiang1 aSmith, M., D.1 aZuo, Xiaoan1 aWang, Zhengwen1 aKnapp, Alan, K.1 aHan, Xingguo1 aCollins, S.L1 aLuo, Wentao uhttps://esajournals.onlinelibrary.wiley.com/doi/10.1002/ecy.422000579nas a2200157 4500008004100000245011800041210006900159300001400228490000800242100003000250700002300280700002300303700001800326700002000344856005700364 2023 eng d00aTraits that distinguish dominant species across aridity gradients differ from those that respond to soil moisture0 aTraits that distinguish dominant species across aridity gradient a311 - 3220 v2011 aGriffin-Nolan, Robert, J.1 aFelton, Andrew, J.1 aSlette, Ingrid, J.1 aSmith, M., D.1 aKnapp, Alan, K. uhttps://link.springer.com/10.1007/s00442-023-05315-y02601nas a2200265 4500008004100000245007800041210006900119300001600188490000800204520179500212100002002007700001702027700003002044700002102074700002702095700002002122700002102142700001402163700002102177700002302198700001802221700001402239700002302253856005902276 2020 eng d00aResolving the Dust Bowl paradox of grassland responses to extreme drought0 aResolving the Dust Bowl paradox of grassland responses to extrem a22249-222550 v1173 a

During the 1930s Dust Bowl drought in the central United States, species with the C3 photosynthetic pathway expanded throughout C4-dominated grasslands. This widespread increase in C3 grasses during a decade of low rainfall and high temperatures is inconsistent with well-known traits of C3 vs. C4 pathways. Indeed, water use efficiency is generally lower, and photosynthesis is more sensitive to high temperatures in C3 than C4 species, consistent with the predominant distribution of C3 grasslands in cooler environments and at higher latitudes globally. We experimentally imposed extreme drought for 4 y in mixed C3/C4 grasslands in Kansas and Wyoming and, similar to Dust Bowl observations, also documented three- to fivefold increases in C3/C4 biomass ratios. To explain these paradoxical responses, we first analyzed long-term climate records to show that under nominal conditions in the central United States, C4 grasses dominate where precipitation and air temperature are strongly related (warmest months are wettest months). In contrast, C3 grasses flourish where precipitation inputs are less strongly coupled to warm temperatures. We then show that during extreme drought years, precipitation–temperature relationships weaken, and the proportion of precipitation falling during cooler months increases. This shift in precipitation seasonality provides a mechanism for C3 grasses to respond positively to multiyear drought, resolving the Dust Bowl paradox. Grasslands are globally important biomes and increasingly vulnerable to direct effects of climate extremes. Our findings highlight how extreme drought can indirectly alter precipitation seasonality and shift ecosystem phenology, affecting function in ways not predictable from key traits of C3 and C4 species.

1 aKnapp, Alan, K.1 aChen, Anping1 aGriffin-Nolan, Robert, J.1 aBaur, Lauren, E.1 aCarroll, Charles, J.W.1 aGray, Jesse, E.1 aHoffman, Ava, M.1 aLi, Xiran1 aPost, Alison, K.1 aSlette, Ingrid, J.1 aCollins, S, L1 aLuo, Yiqi1 aSmith, Melinda, D. uhttp://www.pnas.org/lookup/doi/10.1073/pnas.192203011703509nas a2200313 4500008004100000245008500041210006900126300001600195490000800211520253200219653000902751653001902760653003002779653001202809653002502821653002802846100003002874700002102904700002402925700002402949700002102973700002302994700002403017700001603041700002503057700002003082700001703102856007603119 2019 eng d00aShifts in plant functional composition following long-term drought in grasslands0 aShifts in plant functional composition following longterm drough a2133 - 21480 v1073 a

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

10aANPP10aClimate change10acommunity weighted traits10aDrought10aFunctional diversity10aplant functional traits1 aGriffin-Nolan, Robert, J.1 aBlumenthal, D.M.1 aCollins, Scott., L.1 aFarkas, Timothy, E.1 aHoffman, Ava, M.1 aMueller, Kevin, E.1 aOcheltree, Troy, W.1 aSmith, M.D.1 aWhitney, Kenneth, D.1 aKnapp, Alan, K.1 aJones, Holly uhttps://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2745.1325202388nas a2200205 4500008004100000022001400041245010800055210006900163300001400232490000800246520170300254100003001957700002801987700002202015700002602037700002402063700001602087700002002103856005902123 2018 eng d a1385-023700aLegacy effects of a regional drought on aboveground net primary production in six central US grasslands0 aLegacy effects of a regional drought on aboveground net primary  a505 - 5150 v2193 a

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

1 aGriffin-Nolan, Robert, J.1 aCarroll, Charles, J. W.1 aDenton, Elsie, M.1 aJohnston, Melissa, K.1 aCollins, Scott., L.1 aSmith, M.D.1 aKnapp, Alan, K. uhttp://link.springer.com/10.1007/s11258-018-0813-7.pdf03181nas a2200289 4500008004100000245012300041210006900164300001600233490000700249520223100256100003002487700002202517700002802539700002002567700001802587700002102605700002102626700002102647700002302668700002002691700002102711700002402732700002202756700002002778700001702798856007602815 2018 eng d00aTrait selection and community weighting are key to understanding ecosystem responses to changing precipitation regimes0 aTrait selection and community weighting are key to understanding a1746 - 17560 v323 a

1. Plant traits can be used to predict ecosystem responses to environmental change using a response–effect trait framework. To do this, appropriate traits must be identified that explain a species' influence on ecosystem function (“effect traits”) and the response of those species to environmental change (“response traits”). Response traits are often identified and measured along gradients in plant resources, such as water availability; however, precipitation explains very little variation in most plant traits globally. Given the strong relationship between plant traits and ecosystem functions, such as net primary productivity (NPP), and between NPP and precipitation, the lack of correlation between precipitation and plant traits is surprising.

2. We address this issue through a systematic review of >500 published studies that describe plant trait responses to altered water availability. The overarching goal of this review was to identify potential causes for the weak relationship between commonly measured plant traits and water availability so that we may identify more appropriate “response traits.”

3. We attribute weak trait–precipitation relationships to an improper selection of traits (e.g., nonhydraulic traits) and a lack of trait‐based approaches that adjust for trait variation within communities (only 4% of studies measure community‐weighted traits). We then highlight the mechanistic value of hydraulic traits as more appropriate “response traits” with regard to precipitation, which should be included in future community‐scale trait surveys.

4. Trait‐based ecology has the potential to improve predictions of ecosystem responses to predicted changes in precipitation; however, this predictive power depends heavily on the identification of reliable response and effect traits. To this end, trait surveys could be improved by a selection of traits that reflect physiological functions directly related to water availability with traits weighted by species relative abundance.

1 aGriffin-Nolan, Robert, J.1 aBushey, Julie, A.1 aCarroll, Charles, J. W.1 aChallis, Anthea1 aChieppa, Jeff1 aGarbowski, Magda1 aHoffman, Ava, M.1 aPost, Alison, K.1 aSlette, Ingrid, J.1 aSpitzer, Daniel1 aZambonini, Dario1 aOcheltree, Troy, W.1 aTissue, David, T.1 aKnapp, Alan, K.1 aFox, Charles uhttps://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2435.13135