@article {6068, title = {Repeated extreme droughts decrease root production, but not the potential for post-drought recovery of root production, in a mesic grassland}, journal = {Oikos}, volume = {1}, year = {2023}, pages = {e08899}, abstract = {

Global climate change is expected to cause more frequent extreme droughts in many parts of the world. Despite the crucial role of roots in water acquisition and plant survival, our understanding of ecosystem vulnerability to drought is primarily based on aboveground impacts. As return intervals between droughts decrease, root responses to one drought might alter responses to subsequent droughts, but this remains unresolved. We conducted a seven-year experiment that imposed extreme drought (growing season precipitation reduced 66\%) in a mesic grassland. Plots were droughted during years 1\–2 (\‘Drought 1\&$\#$39;), or years 5\–6 (\‘Drought 2\&$\#$39;) or both. We quantified root production during year 6 (final year of Drought 2) and year 7 (first year after Drought 2), when all plots received ambient precipitation. We found that repeated drought decreased root mass production more than twice as much as a single drought (\−63\% versus \−27\%, respectively, relative to ambient precipitation). Root mass production of the dominant C4 grass Andropogon gerardii did not decrease significantly with either one or two droughts. A. gerardii root traits differed from subdominant species on average across all treatments, but drought did not alter root traits of either A. gerardii or the subdominant species (collectively). In year 6, root production in plots droughted 4 years ago had not recovered (\−21\% versus control), but root production recovered in all formerly droughted plots in year 7, when precipitation was above average. Our results highlight the complexity of root responses to drought. Drought-induced reductions in root production can persist for years after drought and repeated drought can reduce production even further, but this does not preclude rapid recovery of root production in a wet year.

}, keywords = {LTER-KNZ}, doi = {10.1111/oik.08899}, url = {https://onlinelibrary.wiley.com/doi/10.1111/oik.08899}, author = {Slette, I.J. and D.L. Hoover and M. D. Smith and Knapp, A.K.} } @article {5956, title = {Deconstructing precipitation variability: rainfall event size and timing uniquely alter ecosystem dynamics}, journal = {Journal of Ecology}, volume = {109}, year = {2021}, pages = {3356-3369}, abstract = {}, keywords = {LTER-KNZ}, doi = {10.1111/1365-2745.13724}, url = {https://onlinelibrary.wiley.com/doi/10.1111/1365-2745.13724}, author = {Griffin-Nolan, R.J. and Slette, I.J. and Alan K. Knapp} } @article {KNZ002034, title = {Is a drought a drought in grasslands? Productivity responses to different types of drought}, journal = {Oecologia}, year = {2021}, keywords = {LTER-KNZ}, author = {Carroll, C.J.W. and Slette, I.J. and Griffin-Nolan, R.J. and Baur, L.E. and Hoffman, A.M. and Denton, E.M. and Gray, J.E. and Post, A.K. and Johnston, M.K. and Yu, Q. and Collins, S.L. and Luo, Y. and Smith, M.D. and Knapp, A.K.} } @article {5993, title = {Effects of compounded precipitation pattern intensification and drought occur belowground in a mesic grassland}, journal = {Ecosystems}, year = {2021}, abstract = {

Climate change is altering precipitation regimes globally, with expectations of intensified precipitation patterns (for example, larger but fewer rainfall events) and more frequent and extreme drought. Both aspects of precipitation change can impact ecosystem function individually, but it is more likely that they will occur in combination. In a central US mesic grassland, we imposed an extreme 2-year drought (growing season precipitation reduced by 66\%) on plots with a long-term (16-year) history of exposure to either ambient or intensified precipitation patterns (average threefold increase in event size and threefold decrease in event number during the growing season). While this intensified pattern did not alter total precipitation amount, it generally led to ecosystem responses consistent with a drier environment (for example, reduced soil moisture, aboveground net primary production (ANPP), and soil CO2 flux, but little evidence for altered root biomass). Surprisingly, this history of intensified precipitation patterns did not affect the response of ANPP to the subsequent extreme drought. In contrast, previous exposure to intensified precipitation patterns reduced root production and muted soil CO2 flux responses to rainfall events during drought. Reduced root production in plots experiencing compounded precipitation extremes was driven not by the dominant C4 grass species, Andropogon gerardii, but collectively by the subdominant species in the plant community. Overall, our results reveal that compound changes in precipitation patterns and amount affected this grassland in ways that were less apparent (that is, belowground) than responses to either change individually and significantly reduced ecosystem carbon uptake.

}, keywords = {LTER-KNZ}, doi = {10.1007/s10021-021-00714-9}, url = {https://doi.org/10.1007/s10021-021-00714-9}, author = {Slette, I.J. and J. M. Blair and Fay, P.A. and M. D. Smith and Alan K. Knapp} } @phdthesis {6060, title = {Impacts of compound precipitation extremes on belowground dynamics in a mesic grassland}, volume = {PhD Dissertation}, year = {2021}, type = {Ph.D. Thesis}, keywords = {LTER-KNZ}, url = {https://mountainscholar.org/handle/10217/234322}, author = {Slette, I.J.} } @article {KNZ001887, title = {A reality check for climate change experiments: Do they reflect the real world?}, journal = {Ecology}, volume = {99}, year = {2018}, pages = {2145-2151}, abstract = {

Experiments are widely used in ecology, particularly for assessing global change impacts on ecosystem function. However, results from experiments often are inconsistent with observations made under natural conditions, suggesting the need for rigorous comparisons of experimental and observational studies. We conducted such a \“reality check\” for a grassland ecosystem by compiling results from nine independently conducted climate change experiments. Each experiment manipulated growing season precipitation (GSP) and measured responses in aboveground net primary production (ANPP). We compared results from experiments with long-term (33-yr) annual precipitation and ANPP records to ask if collectively (n\ =\ 44 experiment-years) experiments yielded estimates of ANPP, rain-use efficiency (RUE, grams per square meter ANPP per mm precipitation), and the relationship between GSP and ANPP comparable to observations. We found that mean ANPP and RUE from experiments did not deviate from observations. Experiments and observational data also yielded similar functional relationships between ANPP and GSP, but only within the range of historically observed GSP. Fewer experiments imposed extreme levels of GSP (outside the observed 33-yr record), but when these were included, they altered the GSP\–ANPP relationship. This result underscores the need for more experiments imposing extreme precipitation levels to resolve how forecast changes in climate regimes will affect ecosystem function in the future.

}, keywords = {LTER-KNZ}, doi = {10.1002/ecy.2474}, url = {https://esajournals.onlinelibrary.wiley.com/doi/epdf/10.1002/ecy.2474}, author = {Alan K. Knapp and Carroll, C.J.W. and Griffin-Nolan, R.J. and Slette, I.J. and Chavez, F.A. and Baur, L. and Felton, A.J. and Gray, J. and Hoffman, A.M. and Lemoine, N.P. and Mao, W. and Post, A. and M.D. Smith} } @article {KNZ001783, title = {Pushing precipitation to the extremes in distributed experiments: recommendations for simulating wet and dry years}, journal = {Global Change Biology}, volume = {23}, year = {2017}, pages = {1774-1782}, abstract = {

Intensification of the global hydrological cycle, ranging from larger individual precipitation events to more extreme multiyear droughts, has the potential to cause widespread alterations in ecosystem structure and function. With evidence that the incidence of extreme precipitation years (defined statistically from historical precipitation records) is increasing, there is a clear need to identify ecosystems that are most vulnerable to these changes and understand why some ecosystems are more sensitive to extremes than others. To date, opportunistic studies of naturally occurring extreme precipitation years, combined with results from a relatively small number of experiments, have provided limited mechanistic understanding of differences in ecosystem sensitivity, suggesting that new approaches are needed. Coordinated distributed experiments (CDEs) arrayed across multiple ecosystem types and focused on water can enhance our understanding of differential ecosystem sensitivity to precipitation extremes, but there are many design challenges to overcome (e.g., cost, comparability, standardization). Here, we evaluate contemporary experimental approaches for manipulating precipitation under field conditions to inform the design of \‘Drought-Net\’, a relatively low-cost CDE that simulates extreme precipitation years. A common method for imposing both dry and wet years is to alter each ambient precipitation event. We endorse this approach for imposing extreme precipitation years because it simultaneously alters other precipitation characteristics (i.e., event size) consistent with natural precipitation patterns. However, we do not advocate applying identical treatment levels at all sites \– a common approach to standardization in CDEs. This is because precipitation variability varies \>fivefold globally resulting in a wide range of ecosystem-specific thresholds for defining extreme precipitation years. For CDEs focused on precipitation extremes, treatments should be based on each site\&$\#$39;s past climatic characteristics. This approach, though not often used by ecologists, allows ecological responses to be directly compared across disparate ecosystems and climates, facilitating process-level understanding of ecosystem sensitivity to precipitation extremes.

}, keywords = {LTER-KNZ}, doi = {10.1111/gcb.13504}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.13504}, author = {Alan K. Knapp and M.L. Avolio and Beier, C. and Carroll, C.J.W. and Scott. L. Collins and Dukes, J.S. and Fraser, L.H. and Griffin-Nolan, R.J. and Hoover, D.L. and Jentsch, A. and Loik, M.E. and Phillips, R.P. and Post, A.K. and Sala, O.E. and Slette, I.J. and Yahdjian, L. and M.D. Smith} }