Conclusion
In our study, we sought to determine whether the widespread keystone grass, Themada triandra , relied on soil microbiota from arid locations to gain growth advantages when grown under drought conditions. We report that soil microbiota from more arid sources had strong positive effects on plant growth under drought conditions. We also show that soil aridity, water stress, and sterilisation treatments shaped both plant growth and the soil-to-endosphere recruitment as described by the two-step selection process. Finally, soil physicochemical variables associated with our stress and sterilisation conditions influenced the composition of bacterial communities far more strongly that the presence of T. triandra plants. Together, these results highlight that grassland decline by increased aridity due to climate change may be in part mitigated by the effects of healthy soil microbiota on keystone grass species. As such, we anticipate that soil-based manipulations to enhance the restoration of climate-resilient grasslands will be increasingly applicable to future interventions in grassland ecosystems.