Drought duration does not impact soil microbiome resilience

Increasing global droughts exert large but poorly understood effects on the microbial communities and ecology of soil. Microbial communities generally show resilience and return to pre-drought conditions when short-term droughted soils are rewet; soils exposed to long-term drought, however, often show a lag upon rewetting, after which microbial communities may or may not return to their pre-stressed conditions. Though short-term droughts have been widely studied, long-term drought manipulation experiments remain rare, especially those that compare microbial response to short-term and long-term drought in tandem. We conducted a 1000-day drought simulation in controlled laboratory conditions with soil cores collected from a tidal freshwater ecosystem in Washington state, USA, and subsequently exposed them to rewetting for two weeks. We also included short-term (30-day and 90-day) drought and rewet treatments to directly compare microbial community and organic matter responses across drought durations. We found distinct microbial taxa belonging to Firmicutes and Actinobacteria enriched after the 1000-day drought, but not after the short-term droughts. While we hypothesized that the microbial community would recover from a short-term drought after rewetting to resemble pre-drought conditions, our results revealed community dissimilarities between rewet and pre-drought conditions across all drought durations. These findings suggest unique microbial life history strategies within certain microbial phyla that make them successful colonizers during an extended drought period, and the influence of environmental and physiological context on microbial responses to rewetting. ImportanceDroughts are increasing in frequency and intensity globally with severe implications for ecosystem services and soil functions. It is important to understand how long-term drought impacts soil microbial communities and organic matter chemistry to better predict future ecosystem responses to sustained moisture deficit conditions. We subjected soils to short-term (30 and 90 days) and long-term (1000 days) drought treatments and subsequently rewetted them to understand microbiome recovery to pre-drought conditions. Our results showed that prolonged drought drastically changes the microbial community and soil organic matter profile compared to short-term drought. While we expected the soil microbiome to recover upon rewetting after short-term drought, our results showed an altered microbiome composition, compared to pre-drought conditions, for both short-and long-term drought, suggesting microbial responses to soil rewetting was independent of drought duration imposed. These results provide important insights into soil biological and chemical functions that remain sensitive to change under fluctuating soil moisture conditions and future drought scenarios.