Long-term warming and vegetation change have no impact on microbial resistance to drought, but destabilise microbial communities and microbially-mediated functions

Climate change presents multiple stresses to ecosystems that operate over different timescales, such as long-term warming and short-term drought. It is well established that soil microbial communities are highly responsive to individual stresses, but how they respond combined warming and drought, and how factors such as vegetation change moderate responses, remains uncertain. Here we tested whether long-term passive warming modifies the resistance (amplitude of response) and resilience (degree and duration of recovery) of soil microbial communities to short-term drought. We also tested whether warming effects on microbial resilience to drought are moderated by vegetation composition, and specifically the presence of ericaceous dwarf shrubs, the dominant vegetation type of peatland. This was tested using soil from a nine-year warming and vegetation manipulation experiment established on blanket peatland in northern England. We completed a subsequent laboratory study designed to quantify resistance and resilience of microbial communities and microbial-mediated functions to drought. Neither long-term warming nor shrub removal impacted the resistance of microbial communities to drought. However, resilience of bacterial diversity to drought was decreased by warming (fold change 0.38) and shrub removal (fold change 0.27). Notably the interaction between warming and shrub removal resulted in higher resilience of bacterial diversity than individual treatments (fold change 0.58; warming x shrub removal: p = 0.008). Further, warming and shrub removal individually increased the diversity of fungal communities, and reduced resilience of fungal diversity to drought (fold change of warmed against unwarmed 0.11, shrub removal against control 0.39, combination against control 0.59; warming x shrub removal p = 0.006). Warming also strongly decreased resilience, but not resistance, of nitrogen-based functions to drought, although shrub removal dampened this effect. Our findings demonstrate potential for long-term warming and vegetation change to modify microbial responses to extreme drought events, with implications for peatland carbon and nitrogen cycling under future climate scenarios.