Drought Intensity Shapes Soil Legacy Effects on Grassland Plant and Soil Microbial Communities and Their Responses to Future Drought

Drought can have long-lasting legacy effects on terrestrial ecosystems via persistent shifts in soil microbial community structure and function. Yet, the role drought intensity plays in the formation of soil-mediated drought legacies and in determining plant and microbial responses to subsequent droughts is unknown. Here, we evaluate how soil-mediated drought legacies shaped by the intensity of an initial drought event influence plant and microbial communities in the following year and their response to a subsequent experimental drought. We determined these responses in two model grassland communities with contrasting resource acquisition strategies. We found that the intensity of the initial (i.e., past) drought shaped the composition, network structure and functioning of soil microbial communities, with stronger effects on prokaryotes than fungi. Moreover, drought intensity determined soil-mediated legacy effects on plant responses to a subsequent drought: increasing past drought intensity decreased the drought resistance of the slow-strategy plant community and reduced productivity overshoot in the fast-strategy community after re-wetting. Our findings demonstrate that increasing drought intensity can lead to distinct legacies in soil microbial community composition and function with impacts on plant responses to future droughts.