Multi‐year drought alters plant species composition more than productivity across northern temperate grasslands

Abstract

1. The occurrence of multi-year drought is predicted to increase globally with climate change. However, it is unclear whether drought effects on ecosystems are progressive through time.2. Here, we experimentally reduced growing season precipitation (GSP) by 45% at seven North American temperate grasslands for four consecutive years to determine the following: (a) whether the effects of reduced precipitation on plant community structure and biomass components (shoot, root, litter) are compounding over time; (b) whether prior year climatic and soil conditions influence subsequent drought impacts on plant community structure and biomass components; and (c) whether the effects of reduced precipitation on individual ecosystem components are related to one another.3. Across the seven field sites, we observed neither consistent nor progressive effects of reduced precipitation on any biomass component during the experiment, despite having extreme drought conditions imposed for four consecutive years.Relative to the ambient treatment, above-ground net primary productivity (ANPP) declined in response to drought during the early years of the experiment but increased above the ambient treatment in the fourth year, while root and litter biomass were stable across the sites throughout the study. Similarly, graminoid cover decreased initially but recovered by the final year of the experiment, contributing to observed differences in species composition between treatments across sites.Compositional changes were not associated with any declines in species richness or evenness. Divergent responses among years were not driven by lag effects based on prior year climatic and soil conditions. Furthermore, precipitation effects on ecosystem components were largely independent as we found only two positive links: between ANPP and plant species richness, and between species evenness and composition. 4. Synthesis. Overall, our results suggest that these northern grasslands are relatively resistant to short-term multi-year drought in the context of supporting plant diversity and biomass production.

Plant responses to soil biota depend on precipitation history, plant diversity, and productivity

“…Plant productivity at the field experiment sites ranged from 33.6 to 492.3 g/m 2 and species richness from 4.0 to 18.0 species/ m 2 , with no relationship between the two community characteristics among sites (see Appendix S1: Figure S2). Previous research using a subset of these sites also found no effect of drought on plant diversity and inconsistent effects on productivity (Batbaatar et al, 2021), suggesting that precipitation history, diversity, and productivity effects on SBRs may be evaluated independently. We calculated the treatment averages of total biomass, the root mass fraction, as well as Pascopyrum and Vicia biomass by field site.…”

“…That SBRs were typically positive but independent of soil origin suggests that Vicia may not be specific in its association with beneficial soil microbes. This suggests that subordinate species may be able to compensate for drought legacy effects if the dominant species relies on drought sensitive soil biota (Mariotte et al, 2015), which can result in altered plant composition as seen in the field for a subset of our sites (Batbaatar et al, 2021). That Vicia was strongly affected by drought in both live and sterile soils, however, suggests soil biota benefits are insufficient to allow persistence through drought.…”

“…Plant responses to soil biota are often dependent on the plant species as well as the environmental and community contexts (Baxendale et al, 2014; Bennett & Klironomos, 2019; Harrison & Bardgett 2010). Different components of plant communities therefore likely will possess divergent responses to drought and drought‐conditioned soil biota, which may complicate predictions of drought effects on community structure and function (Batbaatar et al, 2021; van der Putten et al, 2016). Understanding how drought affects SBRs and the consequences for plant communities therefore requires studying how these factors alter plant survival and growth within a community context.…”

Field experiments have enhanced our understanding of drought impacts on terrestrial ecosystems—But where do we go from here?

“…Similarly, numerous studies show that drought alters plant community diversity in many ways (genetic, species, functional and growth form). These studies often infer that plant community attributes, before and after drought, mediate drought sensitivity (Batbaatar et al., 2022; Gottschall et al., 2023; Griffin‐Nolan, Blumenthal, et al., 2019; Harrison et al., 2018; Korell et al., 2021; Liu, Wang, et al., 2022; Mackie et al., 2019; Peñuelas et al., 2007; Shaw et al., 2022; Tilman & El Haddi, 1992; Van Ruijven & Berendse, 2010). Some experiments have explicitly tested for interactions between various components of biodiversity and drought via the independent manipulation of both (e.g.…”

Grassland sensitivity to drought is related to functional composition across East Asia and North America

“…The ecological impacts of drought are most often assessed from single site‐level studies of natural drought (Ignacio et al, 2022) or, less often, across multiple sites spanning a regional precipitation gradient (Batbaatar et al, 2021; Cherwin & Knapp, 2012; Knapp et al, 2015). However, the sensitivity of grasslands to extreme drought is expected to differ between sites, regions, and continents, given their differences in evolutionary history, community structure, precipitation regimes, temperature variability, and soil properties (Smith et al, 2022).…”