A reality check for climate change experiments: Do they reflect the real world?

Knapp, Alan K.; Carroll, Charles J. W.; Griffin‐Nolan, Robert J.; Slette, Ingrid J.; Chaves, Francis A.; Baur, Lauren E.; Felton, Andrew J.; Gray, Jesse E.; Hoffman, Ava M.; Lemoine, Nathan P.; Mao, Wei; Post, Alison K.; Smith, Melinda D.

doi:10.1002/ecy.2474

Cited by 44 publications

(49 citation statements)

References 55 publications

(91 reference statements)

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“…Therefore, we are confident that variation in GSP, and by extension water avail ability, was, and is, the dominant control on primary productivity dynamics within this grassland ecosystem, consistent with previ ous findings (Briggs & Knapp, 1995;Felton, Knapp, & Smith, 2019;Hoover et al, 2014a). Our work underscores the validity and com plimentary nature and utilizes longterm data to interpret ecological experiments (Knapp et al, 2018).…”

Section: Discussionsupporting

confidence: 86%

Precipitation amount and event size interact to reduce ecosystem functioning during dry years in a mesic grassland

Felton

Slette

Smith

et al. 2019

Global Change Biology

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Ongoing intensification of the hydrological cycle is altering rainfall regimes by increasing the frequency of extreme wet and dry years and the size of individual rainfall events. Despite long‐standing recognition of the importance of precipitation amount and variability for most terrestrial ecosystem processes, we lack understanding of their interactive effects on ecosystem functioning. We quantified this interaction in native grassland by experimentally eliminating temporal variability in growing season rainfall over a wide range of precipitation amounts, from extreme wet to dry conditions. We contrasted the rain use efficiency (RUE) of above‐ground net primary productivity (ANPP) under conditions of experimentally reduced versus naturally high rainfall variability using a 32‐year precipitation–ANPP dataset from the same site as our experiment. We found that increased growing season rainfall variability can reduce RUE and thus ecosystem functioning by as much as 42% during dry years, but that such impacts weaken as years become wetter. During low precipitation years, RUE is lowest when rainfall event sizes are relatively large, and when a larger proportion of total rainfall is derived from large events. Thus, a shift towards precipitation regimes dominated by fewer but larger rainfall events, already documented over much of the globe, can be expected to reduce the functioning of mesic ecosystems primarily during drought, when ecosystem processes are already compromised by low water availability.

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Section: Discussionsupporting

confidence: 86%

Precipitation amount and event size interact to reduce ecosystem functioning during dry years in a mesic grassland

Felton

Slette

Smith

et al. 2019

Global Change Biology

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“…In this study, our results showed clear evidence for the nonlinear BNPP-precipitation relationship (Fig. 3b; Appendix S1: Table S2), along with a similar nonlinear ANPP-precipitation relationship that has been frequently observed in previous studies (Bai et al 2008, Gherardi and Sala 2015, Zhang et al 2017c, Knapp et al 2018. As precipitation increased, the saturated response of soil environmental factors (mean and variability of soil-water content, soil temperature, and nitrogen availability) contributed to the nonlinear increase of ecosystem productivity.…”

Section: Nonlinear Response Of Npp and Its Allocation To Changing Presupporting

confidence: 88%

“…Even if some variables, such as ANPP of shallow-rooted species, showed increasing sensitivity to drought treatments over time, they seemed to be more attributed to the declining ambient precipitation. These results suggest that plants are much more responsive to the current changing precipitation rather than cumulative effects, indicating the validity of the experimental approach in studying the influence of changing precipitation on ecosystem functioning (Knapp et al 2018).…”

Section: Bnpp Vertical Redistribution Maintains Plants' Water Acquisimentioning

confidence: 85%

“…, Knapp et al. ). Thus, the increased ANPP proportion of shallow‐rooted species (from 30 to 39% in P−60 plots and P+60 plots) contributed more BNPP in the surface soil as precipitation increased.…”

Section: Discussionmentioning

confidence: 99%

“…), and occur mostly in water‐limited regions where ecosystems are sensitive to changing precipitation (Knapp et al. , Wu et al. ).…”

Section: Introductionmentioning

confidence: 99%

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Plants alter their vertical root distribution rather than biomass allocation in response to changing precipitation

Zhang

Cadotte

Chen

et al. 2019

Ecology

104

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Elucidating the variation of allocation pattern of ecosystem net primary productivity (NPP) and its underlying mechanisms is critically important for understanding the changes of aboveground and belowground ecosystem functions. Under optimal partitioning theory, plants should allocate more NPP to the organ that acquires the most limiting resource, and this expectation has been widely used to explain and predict NPP allocation under changing precipitation. However, confirmatory evidence for this theory has mostly come from observed spatial variation in the relationship between precipitation and NPP allocation across ecosystems, rather than directly from the influences of changing precipitation on NPP allocation within systems. We performed a 6‐yr five‐level precipitation manipulation experiment in a semiarid steppe to test whether changes in NPP allocation can be explained by the optimal partitioning theory, and how water requirement of plant community is maintained if NPP allocation is unaltered. The 30 precipitation levels (5 levels × 6 yr) were divided into dry, nominal, and wet precipitation ranges, relative to historical precipitation variation over the past six decades. We found that NPP in both aboveground (ANPP) and belowground (BNPP) increased nonlinearly as precipitation increased, while the allocation of NPP to BNPP (fBNPP) showed a concave quadratic relationship with precipitation. The declined fBNPP as precipitation increased in the dry range supported the optimal partitioning theory. However, in the nominal range, NPP allocation was not influenced by the changed precipitation; instead, BNPP was distributed more in the surface soil horizon (0–10 cm) as precipitation increased, and conversely more in the deeper soil layers (10–30 cm) as precipitation decreased. This response in root foraging appears to be a strategy to satisfy plant water requirements and partially explains the stable NPP allocation patterns. Overall, our results suggest that plants can adjust their vertical BNPP distribution in response to drought stress, and that only under extreme drought does the optimal partitioning theory strictly apply, highlighting the context dependency of the adaption and growth of plants under changing precipitation.

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Invasive annual grass interacts with drought to influence plant communities and soil moisture in dryland restoration

Garbowski

Johnston

Baker³

et al. 2021

Ecosphere

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Understanding the combined effects of drought and invasive species on plant community development and soil moisture could provide valuable insight into the mechanisms hindering successful native plant establishment in dryland restoration projects. We implemented a re-vegetation experiment at two sites in Colorado, USA (one each in the Western Great Plains and Cold Desert ecoregions) to investigate the effects of drought (66% reduction of ambient growing season rainfall), non-native Bromus tectorum seed addition (465 seeds/m 2), and superabsorbent polymer soil amendment (25 g/m 2) on plant community development and soil volumetric water content at 5 and 30 cm depth. Drought resulted in higher B. tectorum cover at the Western Great Plains site but lower B. tectorum cover at the Cold Desert site. These contrasting results suggest drought may interact with site-specific precipitation patterns to influence B. tectorum establishment. At the Western Great Plains site, drought reduced seeded forb cover and B. tectorum seed addition reduced seeded grass cover, highlighting how the effects of drought and invasive species may vary depending on which functional group is assessed. At the Cold Desert site, drought and B. tectorum seed addition each decreased seeded species cover from approximately 8% to 3%. Superabsorbent polymer effects were limited to slight increases in overall seeded grass cover at the Western Great Plains site from 2.2% to 4.9%. Both drought and B. tectorum seed addition reduced soil volumetric water content but in some cases effects depended on interactions between the two treatments, site, or soil depth. Notably, at the Cold Desert site the reduction in soil volumetric water content resulting from B. tectorum seed addition with ambient precipitation exceeded that of the drought treatment alone at 5 and 30 cm depth. Our results demonstrate that drought and invasive species both negatively influence native plant establishment and soil moisture, and in some cases may interact. Considering both abiotic and biotic stressors as well as their interactions in restoration planning could improve our understanding of native plant establishment and improve re-vegetation outcomes.

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A reality check for climate change experiments: Do they reflect the real world?

Cited by 44 publications

References 55 publications

Precipitation amount and event size interact to reduce ecosystem functioning during dry years in a mesic grassland

Precipitation amount and event size interact to reduce ecosystem functioning during dry years in a mesic grassland

Plants alter their vertical root distribution rather than biomass allocation in response to changing precipitation

Invasive annual grass interacts with drought to influence plant communities and soil moisture in dryland restoration

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