Soil texture mediates microbial assembly and network organization under moisture stress

Background Climate-driven changes in moisture are expected to intensify environmental selection in soils, yet the extent to which soil texture modifies microbial responses to moisture stress remains poorly understood. Because soil texture governs water retention, nutrient diffusion, and habitat structure, it may fundamentally influence how microbial communities assemble and function under drought. Here, we investigated how moisture and soil texture interact to shape bacterial and fungal rhizosphere communities associated with Andropogon virginicus , a drought-tolerant wild relative of maize, across 28 natural field sites in the southeastern United States. Results Soil texture explained greater variation in microbial community composition than moisture stress alone, while moisture-texture interactions produced distinct community structures across sites. Distance-based redundancy (dbRDA) analyses identified soil nitrogen pools, pH, organic matter, and micronutrients as major environmental drivers. Community assembly analyses showed that xeric conditions strengthened deterministic assembly in bacterial communities through increased homogeneous selection, whereas fungal communities remained predominantly stochastic across textures. Moisture-texture interactions also restructured microbial co-occurrence networks, with bacterial networks under xeric conditions exhibiting greater connectivity, competitive interactions, and phylogenetic clustering, while fungal networks remained comparatively modular and texture dependent. Predicted functional profiles further revealed texture-dependent shifts in bacterial metabolic pathways and fungal ecological guilds across moisture regimes, indicating coordinated changes in microbial functional organization under drought. Conclusions Our findings demonstrate that soil texture mediates microbial responses to moisture stress by modifying community assembly, ecological interactions, and functional organization rather than simply altering microbial diversity. Bacterial communities exhibited stronger deterministic responses to drought than fungal communities, highlighting contrasting ecological strategies across microbial domains. These results emphasize the importance of integrating soil physical properties with moisture stress when investigating rhizosphere microbiomes and provide ecological insights that may inform microbiome-based strategies for improving crop resilience under increasingly frequent drought conditions.