@article {KNZ001983, title = {Shifts in plant functional composition following long-term drought in grasslands}, journal = {Journal of Ecology}, volume = {107}, year = {2019}, pages = {2133 - 2148}, abstract = {

\ 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.

}, keywords = {LTER-KNZ, ANPP, Climate change, community weighted traits, Drought, Functional diversity, plant functional traits}, doi = {10.1111/1365-2745.13252}, url = {https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2745.13252}, author = {Griffin-Nolan, Robert J. and D.M. Blumenthal and Scott. L. Collins and Farkas, Timothy E. and Hoffman, Ava M. and Mueller, Kevin E. and Ocheltree, Troy W. and M.D. Smith and Whitney, Kenneth D. and Alan K. Knapp}, editor = {Jones, Holly} } @article {KNZ001631, title = {Differential sensitivity to regional-scale drought in six central US grasslands}, journal = {Oecologia}, volume = {177}, year = {2015}, pages = {949 -957}, abstract = {

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.

}, keywords = {LTER-KNZ, Climate change, Functional diversity, Long-term ecological research, Precipitation, Primary production}, doi = {10.1007/s00442-015-3233-6}, url = {https://link.springer.com/article/10.1007\%2Fs00442-015-3233-6}, author = {Alan K. Knapp and Carroll, C.J.W. and Denton, E.M. and Kimberly J. La Pierre and Scott. L. Collins and M.D. Smith} } @article {KNZ001690, title = {Contrasting sensitivities of two dominant C4 grasses to heat waves and drought}, journal = {Plant Ecology}, volume = {215}, year = {2014}, pages = {721 -731}, abstract = {

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.

}, keywords = {LTER-KNZ, Climate change, Climate extremes, Mesic grassland, photosynthesis, productivity}, doi = {10.1007/s11258-014-0345-8}, url = {https://link.springer.com/article/10.1007\%2Fs11258-014-0345-8}, author = {D.L. Hoover and M.D. Smith} } @article {KNZ001532, title = {Rainfall variability has minimal effects on grassland recovery from repeated grazing}, journal = {Journal of Vegetation Science}, volume = {25}, year = {2014}, pages = {36 -44}, abstract = {

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.

}, keywords = {LTER-KNZ, Annual net primary production, Climate change, Clipping, disturbance, diversity, Grass{\textendash}forb interaction, Konza, Precipitation, Stem density}, doi = {10.1111/jvs.12065}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/jvs.12065}, author = {Koerner, S.E. and Scott. L. Collins and John M. Blair and Alan K. Knapp and M.D. Smith} } @article {KNZ001496, title = {Past, present, and future roles of long-term experiments in the LTER Network}, journal = {Bioscience}, volume = {62}, year = {2012}, pages = {377 -389}, abstract = {

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\&$\#$39;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.

}, keywords = {LTER-KNZ, Climate change, global change, long-term research, LTER Network, multifactor experiments}, doi = {10.1525/bio.2012.62.4.9}, url = {https://academic.oup.com/bioscience/article/62/4/377/243762}, author = {Alan K. Knapp and M.D. Smith and Hobbie, S.E. and Scott. L. Collins and Fahey, T.J. and Hansen, G.J.A. and Landis, D.A. and Kimberly J. La Pierre and Melillo, J.M. and Seastedt, T.R. and Shaver, G.R. and Webster, J.R.} } @article {KNZ001187, title = {Consequences of more extreme precipitation regimes for terrestrial ecosystems}, journal = {BioScience}, volume = {58}, year = {2008}, pages = {811 -821}, abstract = {

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.

}, keywords = {LTER-KNZ, Climate change, Drought, Ecosystems, Precipitation, soil water}, doi = {10.1641/B580908}, url = {https://academic.oup.com/bioscience/article/58/9/811/250853}, author = {Alan K. Knapp and Beier, C. and Briske, D.D. and Classen, A.T. and Luo, Y. and Reichstein, M. and M.D. Smith and Smith, S.D. and Bell, J.E. and Fay, P.A. and Heisler, J.L. and Leavitt, S.W and Sherry, R. and Smith, B. and Weng, E.} } @article {KNZ001070, title = {Growth responses of twodominant C4 grass species to altered water availability}, journal = {InternationalJournal of Plant Sciences}, volume = {167}, year = {2006}, pages = {1001 -1010}, abstract = {Identifying 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{\textendash}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.}, keywords = {LTER-KNZ, Andropogon gerardii, biomass allocation, Climate change, leaf turnover, photosynthesis, Sorghastrum nutans, water stress}, doi = {10.1086/505611}, author = {Swemmer, A.M. and Alan K. Knapp and M.D. Smith} }