03509nas 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/10.1111/1365-2745.1325202530nas a2200241 4500008004100000245008400041210006900125300001300194490000800207520176300215653001901978653002501997653003402022653001802056653002302074100002002097700002002117700001702137700002802154700002402182700001602206856006602222 2015 eng d00aDifferential sensitivity to regional-scale drought in six central US grasslands0 aDifferential sensitivity to regionalscale drought in six central a949 -9570 v1773 a

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

10aClimate change10aFunctional diversity10aLong-term ecological research10aPrecipitation10aPrimary production1 aKnapp, Alan, K.1 aCarroll, C.J.W.1 aDenton, E.M.1 aLa Pierre, Kimberly, J.1 aCollins, Scott., L.1 aSmith, M.D. uhttps://link.springer.com/article/10.1007%2Fs00442-015-3233-601969nas a2200193 4500008004100000245008300041210006900124300001300193490000800206520136600214653001901580653002101599653002001620653001901640653001701659100001701676700001601693856006601709 2014 eng d00aContrasting sensitivities of two dominant C4 grasses to heat waves and drought0 aContrasting sensitivities of two dominant C4 grasses to heat wav a721 -7310 v2153 a

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

10aClimate change10aClimate extremes10aMesic grassland10aphotosynthesis10aproductivity1 aHoover, D.L.1 aSmith, M.D. uhttps://link.springer.com/article/10.1007%2Fs11258-014-0345-802943nas a2200277 4500008004100000245008900041210006900130300001100199490000700210520211800217653003402335653001902369653001302388653001602401653001402417653002902431653001002460653001802470653001702488100001802505700002402523700002002547700002002567700001602587856006202603 2014 eng d00aRainfall variability has minimal effects on grassland recovery from repeated grazing0 aRainfall variability has minimal effects on grassland recovery f a36 -440 v253 a

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

10aAnnual net primary production10aClimate change10aClipping10adisturbance10adiversity10aGrass–forb interaction10aKonza10aPrecipitation10aStem density1 aKoerner, S.E.1 aCollins, Scott., L.1 aBlair, John, M.1 aKnapp, Alan, K.1 aSmith, M.D. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/jvs.1206502050nas a2200313 4500008004100000245008100041210006900122300001300191490000700204520112700211653001901338653001801357653002301375653001701398653002801415100002001443700001601463700001701479700002401496700001601520700001901536700001701555700002801572700001801600700001901618700001701637700001801654856006401672 2012 eng d00aPast, present, and future roles of long-term experiments in the LTER Network0 aPast present and future roles of longterm experiments in the LTE a377 -3890 v623 a

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

10aClimate change10aglobal change10along-term research10aLTER Network10amultifactor experiments1 aKnapp, Alan, K.1 aSmith, M.D.1 aHobbie, S.E.1 aCollins, Scott., L.1 aFahey, T.J.1 aHansen, G.J.A.1 aLandis, D.A.1 aLa Pierre, Kimberly, J.1 aMelillo, J.M.1 aSeastedt, T.R.1 aShaver, G.R.1 aWebster, J.R. uhttps://academic.oup.com/bioscience/article/62/4/377/24376202231nas a2200349 4500008004100000245008200041210006900123300001300192490000700205520128800212653001901500653001201519653001501531653001801546653001501564100002001579700001401599700001701613700001801630700001201648700001901660700001601679700001601695700001501711700001401726700001801740700001701758700001501775700001401790700001301804856006401817 2008 eng d00aConsequences of more extreme precipitation regimes for terrestrial ecosystems0 aConsequences of more extreme precipitation regimes for terrestri a811 -8210 v583 a

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

10aClimate change10aDrought10aEcosystems10aPrecipitation10asoil water1 aKnapp, Alan, K.1 aBeier, C.1 aBriske, D.D.1 aClassen, A.T.1 aLuo, Y.1 aReichstein, M.1 aSmith, M.D.1 aSmith, S.D.1 aBell, J.E.1 aFay, P.A.1 aHeisler, J.L.1 aLeavitt, S.W1 aSherry, R.1 aSmith, B.1 aWeng, E. uhttps://academic.oup.com/bioscience/article/58/9/811/25085302107nas a2200229 4500008004100000245008300041210006900124300001500193490000800208520135300216653002401569653002301593653001901616653001801635653001901653653002301672653001701695100001801712700002001730700001601750856011101766 2006 eng d00aGrowth responses of twodominant C4 grass species to altered water availability0 aGrowth responses of twodominant C4 grass species to altered wate a1001 -10100 v1673 aIdentifying key ecophysiological traits that differ among dominant plant species and can be linked to species‐specific responses to drought would improve our ability to forecast community and ecosystem responses to global climate change. The mesic grasslands of the central plains of North America are dominated by two C4 grass species, Andropogon gerardii and Sorghastrum nutans, which purportedly differ in their tolerance of water stress. Individuals of these two species were grown in the field under rain‐out shelters and subjected to wet (watered every 2–3 d) or dry (repeatedly subjected to wilting before watering) soil moisture regimes. A range of ecophysiological traits potentially important for tolerating water stress were concurrently measured. Although few traits differed between the species in the wet treatment, several traits were identified in the dry treatment that may enable A. gerardii to better tolerate drought. These were greater allocation to roots, reduced allocation to flowering, more rapid leaf turnover, and more rapid recovery of photosynthesis after wilting. The latter two traits may be particularly important for coping with increased variability in rainfall regimes in the future and are consistent with recently documented responses of A. gerardii to experimental increases in soil moisture variability.10aAndropogon gerardii10abiomass allocation10aClimate change10aleaf turnover10aphotosynthesis10aSorghastrum nutans10awater stress1 aSwemmer, A.M.1 aKnapp, Alan, K.1 aSmith, M.D. uhttp://lter.konza.ksu.edu/content/growth-responses-twodominant-c4-grass-species-altered-water-availability