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We review results from field experiments that simulate drought, an ecologically impactful global change threat that is predicted to increase in magnitude, extent, duration and frequency. Our goal is to address, from primarily an ecosystem perspective, the questions 'What have we learned from drought experiments?' and 'Where do we go from here?'.Drought experiments are among the most numerous climate change manipulations and have been deployed across a wide range of biomes, although most are conducted in short‐statured, water‐limited ecosystems. Collectively, these experiments have enabled ecologists to quantify the negative responses to drought that occur for most aspects of ecosystem structure and function. Multiple meta‐analyses of responses have also enabled comparisons of relative effect sizes of drought across hundreds of sites, particularly for carbon cycle metrics. Overall, drought experiments have provided strong evidence that ecosystem sensitivity to drought increases with aridity, but that plant traits associated with aridity are not necessarily predictive of drought resistance. There is also intriguing evidence that as drought magnitude or duration increases to extreme levels, plant strategies may shift from drought tolerance to drought escape/avoidance.We highlight three areas where more drought experiments are needed to advance our understanding. First, because drought is intensifying in multiple ways, experiments are needed that address alterations in drought magnitude versus duration, timing and/or frequency (individually and interactively). Second, drivers of drought may be shifting—from precipitation deficits to rising atmospheric demand for water—and disentangling how ecosystems respond to changes in hydrological 'supply versus demand' is critical for understanding drought impacts in the future. Finally, more attention should be focussed on post‐drought recovery periods since legacies of drought can affect ecosystem functioning much longer than the drought itself.We conclude with a call for a fundamental shift in the focus of drought experiments from those designed primarily as 'response experiments', quantifying the magnitude of change in ecosystem structure and function, to more 'mechanistic experiments'—those that explicitly manipulate ecological processes or attributes thought to underpin drought responses. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Plant traits are useful proxies of plant strategies and can influence community and ecosystem responses to climate extremes, such as severe drought. Few studies, however, have investigated both the immediate and lagged effects of drought on community‐weighted mean (CWM) plant traits, with even less research on the relative roles of interspecific vs. intraspecific trait variability in such responses.We experimentally reduced growing season precipitation by 66% in two cold‐semi‐arid grassland sites in northern China for four consecutive years to explore the drought resistance of CWM traits as well as their recovery 2 years following the drought. In addition, we isolated the effects of both interspecific and intraspecific trait variability on shifts in CWM traits.At both sites, we observed significant effects of drought on interspecific and intraspecific trait variability which, in some cases, led to significant changes in CWM traits. For example, drought led to reduced CWM plant height and leaf phosphorous content, but increased leaf carbon content at both sites, with responses primarily due to intraspecific trait shifts. Surprisingly, these CWM traits recovered completely 2 years after the extreme drought. Intraspecific trait variability influenced CWM traits via both positive and negative covariation with interspecific trait variability during drought and recovery phases.These findings highlight the important role of interspecific and intraspecific trait variability in driving the response and recovery of CWM traits following extreme, prolonged drought. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Drought events induced by global climate change strongly modify ecosystem structure and function in grasslands. Higher plant biodiversity can enhance ecosystem resistance to drought; however, the potential effects of drought on the relationships between above‐ground productivity (ANPP) and biodiversity along a natural aridity gradient remain poorly understood.Here, we studied the effects of experimental drought on plant community structure and ANPP during the two different dry years (2015 and 2017) spanning three temperate steppe sites with low‐, medium‐ and high‐aridity levels. We also examined the effects of drought and aridity on the associations of plant species (richness and abundance), functional (community‐weighted trait means and functional dispersion) and phylogenetic diversity (evolutionary lineages) with ANPP. A structural equation modelling (SEM) was used to elucidate how the drought affected ANPP by altering biodiversity attributes.We found that experimental drought shaped the biodiversity–ANPP relationships, and the biodiversity–ANPP relationships differed among three sites. At the low‐aridity site, ANPP was correlated with plant functional traits, whereas ANPP was correlated with functional dispersion, species and phylogenetic diversity at the medium‐aridity site. At the high‐aridity site, ANPP was correlated with species richness, functional traits and phylogenetic diversity. Compared with 2015, natural drought in 2017 strengthened the associations of species diversity, functional dispersion, leaf dry matter content and leaf nitrogen content with ANPP across three sites. SEM further showed that both experimental and natural drought directly decreased ANPP and indirectly decreased ANPP by reducing community‐weighted mean of plant height.Synthesis. These results suggest that the aridity increase or drought occurrence is likely to induce the shifts in the associations of ANPP with species and functional diversity, highlighting the important role of water availability or precipitation conditions in regulating the biodiversity–ANPP relationships in temperate steppes. Overall, functional traits related to plant size play a crucial role in modulating the response of productivity to drought across three steppe sites. Thus, to buffer the negative effects of drought on steppe ANPP should pay attention to protect the species with large plant size. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Intraspecific diversity of dominant species in native plant communities can modulate ecosystem function under both optimal and stressful conditions. Yet, few genotype by environment interaction studies quantify differences in the shape of plasticity functions or phenotypic breakpoints across genotypes in natural populations.Using three genotypes with a history of drought selection, we performed a greenhouse study on the dominant tallgrass prairie species Andropogon gerardii. We investigated phenotypic plasticity and recovery differences among genotypes across a water availability gradient, measuring growth‐related, instantaneous and cumulative phenotypes. To further understand genotype by environment effects, we quantified plasticity functions and breakpoints among genotypes.Like other studies, we found strong evidence for phenotypic and plasticity differences among genotypes. However, we also found nonlinear plasticity functions and breakpoints were common across phenotypes, especially relative growth rates, biomass allocation and root architecture. Drought selected genotypes were also more likely to flower during recovery, but all genotypes were resilient to drought across treatments.We demonstrate that plasticity functions may help explain intraspecific diversity, patterns of selection and nonlinear community responses to more variable rainfall within an experimental population. In particular, plasticity functions can help disentangle drought/variability tolerance versus acquisitive strategies. A better understanding of intraspecific diversity in this grass species will provide more mechanistic insight into its ability to buffer ecosystem changes and provide resiliency in the tallgrass prairie under future droughts. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

The well-described pattern of a few common and many rare species in plant communities (dominance-diversity curves) also has been documented within populations of dominant plant species. Understanding how these common genotypes coexist has implications for how genotype richness of a dominant species may impact community and ecosystem processes. Some studies have shown that increased genotype richness of a dominant species leads to an increase in above-ground productivity, suggesting niche complementarity between genotypes. However, mechanistic understanding of how genotypes may complement one another is lacking., We conducted a pairwise competition experiment between four common and naturally co-occurring genotypes of a dominant C4 grass species, Andropogon gerardii, in tallgrass prairie of the central United States. The genotypes were grown under both intra- and intergenotypic competition with different combinations of resources (low and high light, water, and nitrogen) in the greenhouse., We determined that there were above- and below-ground phenotypic differences between genotypes which results in altered competitive interactions depending on resource conditions. Different genotypes were competitively dominant under low- and high-light conditions and low and high N and water availability. Moreover, relative yield total values ( RYT) for each genotype pairwise combination indicated that all four genotypes make demands on different resources, providing evidence for niche complementarity., Finally, we found that differential success in resource acquisition, biomass accumulation, and subsequent competitive ability translated to variation in vegetative reproductive success of the genotypes, which has implications for the population dynamics of this primarily asexually reproducing perennial grass., Our results suggest that naturally co-occurring genotypes coexist because they are competitively dominant under different environmental conditions, providing insight into how genetic diversity within dominant plant species is maintained and may potentially affect important ecosystem processes. [ABSTRACT FROM AUTHOR]