Results/Conclusions At the community level, the composition of the vegetation at BCCIL is surprisingly resistant to climate treatments, but we observed substantial small-scale turnover in plant species composition within microsites. In particular, the abundance of plant species with high leaf construction costs has increased in drought treatments, which is likely to influence the quality of substrate available to soil microbes. Thus, observed shifts in soil microbial community structure were associated with changes in plant species composition. We measured substantial changes in the abundances of subordinate microbial taxa in drought treatments, which were linked to plant traits representing the quality of available resources. Modified nutrient dynamics in the drought plots can also be associated to changes in plant and soil microbial communities. We suggest that increased supply rates of nitrogen post-drought either indicate higher rates of microbial mineralisation, or reduced plant uptake as a result of lower biomass growth. Although phosphorus supply rates were unaffected by climate treatments, both summer drought and winter warming strengthened the relationship between nitrogen and phosphorus acquiring enzymes, which suggests greater investment of nitrogen in phosphorus acquisition by plants and/or soil microbes. At the population level, observed evolutionary responses mimic functional shifts expected at the species level, including lower specific leaf area under drought in the most abundant plant species. Genomic data also reveal that soil microbes may represent an additional indirect source of selection on plant populations under climate change.
Collectively, 23 years of research at BCCIL provides strong evidence that shifts in trait distributions play a pivotal role in determining the structure and function of a grassland subjected to chronic climate change.