Plant-microbe interactions are critical to ecosystem functioning and result in soil legacies, where plants influence the soil in which they grow affecting the fitness of future generations. Soil legacies are driven in part by the two-step selection process, where soil microbes are recruited from bulk soil into rhizospheres (space around roots) and then into endospheres (within plant roots). However, the potential of these soil legacies to provide host plant drought tolerance is poorly understood. In a drought stress greenhouse trial, we show that arid soil legacies increased the biomass under both drought and control conditions of the keystone grass Themeda triandra. We report strong positive associations between T. triandra biomass and bacterial alpha diversity across soils, rhizospheres and endospheres. These findings show that bacterial soil legacies have an important but underappreciated role in grassland resilience to drought, and could be better harnessed to support resilient grassland restoration efforts.
