Contrasting drought responses in two grassland plant–microbe systems under climate change

Abstract Drought strongly affects plant performance and their associated microbiomes, which can play crucial roles in plant stress resistance. Yet, how drought shapes plant–microbiome interactions under global change—particularly elevated temperature and CO 2 —remains insufficiently understood, especially across distinct plant compartments (leaf endosphere, root endosphere, rhizosphere) that host functionally different microbial assemblages. We examined plant and microbiome responses to a drought intensity gradient under current and future climate scenarios (warming and elevated CO 2 ) in two widespread Central European grasses with contrasting ecological strategies: the stress‐tolerant Festuca rubra and the competitive Lolium perenne . Plants were grown in mesocosms subjected to controlled watering and climate treatments, and we quantified plant biomass, functional traits and composition of bacterial and fungal communities using DNA amplicon sequencing. Festuca showed greater responsiveness to drought, exhibiting higher trait plasticity and more pronounced shifts in its microbial communities—particularly in bacteria—than Lolium . In contrast, Lolium displayed limited trait plasticity, relatively stable microbiomes and consistently higher fungal richness in the rhizosphere. The two species hosted distinct bacterial and fungal compositions, indicating strong species‐specific microbiome structuring. Bacterial richness declined markedly with increasing drought intensity, especially in the root endosphere and rhizosphere, whereas fungal richness remained largely stable. Warming and elevated CO 2 partly mitigated drought‐induced declines in bacterial richness, particularly in the Festuca rhizosphere. Conversely, bacterial community composition in the root endosphere showed stronger moisture‐related differentiation under warming and elevated CO 2 than under current climate. Synthesis . By comparing two contrasting plant strategies across a pronounced soil moisture gradient and two global change scenarios, our study demonstrates how drought and climate jointly shape plant performance and associated microbiomes. These findings highlight the importance of integrating plant functional strategies with microbiome dynamics to better understand and predict grassland responses to shifting precipitation regimes under climate warming and rising atmospheric CO 2 .