@article {6300, title = {Field experiments have enhanced our understanding of drought impacts on terrestrial ecosystems{\textemdash}But where do we go from here?}, journal = {Functional Ecology}, volume = {38}, year = {2024}, pages = {76-97}, keywords = {LTER-KNZ}, doi = {10.1111/1365-2435.14460}, url = {https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2435.14460}, author = {Alan K. Knapp and Condon, Kathleen V. and Folks, Christine C. and Sturchio, Matthew A. and Griffin-Nolan, Robert J. and Kannenberg, Steven A. and Gill, Amy S. and Hajek, Olivia L. and Siggers, J. Alexander and M. D. Smith} } @article {6301, title = {Grassland sensitivity to drought is related to functional composition across East Asia and North America}, journal = {Ecology}, volume = {105}, year = {2024}, pages = {e4220}, keywords = {LTER-KNZ}, doi = {10.1002/ecy.4220}, url = {https://esajournals.onlinelibrary.wiley.com/doi/10.1002/ecy.4220}, author = {Song, Lin and Griffin-Nolan, Robert J. and Muraina, Taofeek O. and Chen, Jiaqi and Te, Niwu and Shi, Yuan and Whitney, Kenneth D. and Zhang, Bingchuan and Yu, Qiang and M. D. Smith and Zuo, Xiaoan and Wang, Zhengwen and Alan K. Knapp and Han, Xingguo and S.L Collins and Luo, Wentao} } @article {6297, title = {Traits that distinguish dominant species across aridity gradients differ from those that respond to soil moisture}, journal = {Oecologia}, volume = {201}, year = {2023}, pages = {311 - 322}, keywords = {LTER-KNZ}, doi = {10.1007/s00442-023-05315-y}, url = {https://link.springer.com/10.1007/s00442-023-05315-y}, author = {Griffin-Nolan, Robert J. and Felton, Andrew J. and Slette, Ingrid J. and M. D. Smith and Alan K. Knapp} } @article {KNZ002028, title = {Resolving the Dust Bowl paradox of grassland responses to extreme drought}, journal = {Proceedings of the National Academy of Sciences}, volume = {117}, year = {2020}, pages = {22249-22255}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {10.1073/pnas.1922030117}, url = {http://www.pnas.org/lookup/doi/10.1073/pnas.1922030117}, author = {Alan K. Knapp and Chen, Anping and Griffin-Nolan, Robert J. and Baur, Lauren E. and Carroll, Charles J.W. and Gray, Jesse E. and Hoffman, Ava M. and Li, Xiran and Post, Alison K. and Slette, Ingrid J. and S L Collins and Luo, Yiqi and Smith, Melinda D.} } @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 {KNZ001885, title = {Legacy effects of a regional drought on aboveground net primary production in six central US grasslands}, journal = {Plant Ecology}, volume = {219}, year = {2018}, pages = {505 - 515}, abstract = {

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.

}, keywords = {LTER-KNZ}, issn = {1385-0237}, doi = {10.1007/s11258-018-0813-7}, url = {http://link.springer.com/10.1007/s11258-018-0813-7.pdf}, author = {Griffin-Nolan, Robert J. and Carroll, Charles J. W. and Denton, Elsie M. and Johnston, Melissa K. and Scott. L. Collins and M.D. Smith and Alan K. Knapp} } @article {KNZ001883, title = {Trait selection and community weighting are key to understanding ecosystem responses to changing precipitation regimes}, journal = {Functional Ecology}, volume = {32}, year = {2018}, pages = {1746 - 1756}, abstract = {

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\&$\#$39; 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.

}, keywords = {LTER-KNZ}, doi = {10.1111/1365-2435.13135}, url = {https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2435.13135}, author = {Griffin-Nolan, Robert J. and Bushey, Julie A. and Carroll, Charles J. W. and Challis, Anthea and Chieppa, Jeff and Garbowski, Magda and Hoffman, Ava M. and Post, Alison K. and Slette, Ingrid J. and Spitzer, Daniel and Zambonini, Dario and Ocheltree, Troy W. and Tissue, David T. and Alan K. Knapp}, editor = {Fox, Charles} }