Spatial patterns and driving mechanisms of bacterial and fungal community assembly in rhizosphere soils of Stipa species across eastern Eurasian steppe

Soil microbial biogeography aims to understand the spatial distribution and assembly mechanisms of microbial communities, yet knowledge integrating multiple spatial scales and varied factors remains poorly understood. As dominant species in the Eurasian steppes, Stipa exhibits distinct patterns of geographical substitution and ecological differentiation, providing key examples to reveal biogeographical patterns of microbial community assembly by exploring relationships among multi-Stipa species with multi-environmental factors at multi-spatial scales. In this study, we used high-throughput sequencing to analyze rhizosphere soil samples of S. baicalensis, S. grandis, S. krylovii, S. klemenzii, and S. glareosa dominating in temperate steppe, and S. bungeana and S. breviflora in warm temperate steppe. Results indicated that temperature and precipitation determined zonal patterns of rhizosphere soil bacterial and fungal communities associated with different Stipa species directly related to steppe vegetation types. Geographic isolation led to extra-zonal patterns among different populations (i.e., sites) of the same Stipa species, resulting in pronounced regional differentiation in bacterial and fungal communities. Changes in soil properties due to uneven resource distribution enhanced the spatial heterogeneity of microbial community structures at the local scale. Bacterial community assembly was governed by stochastic processes, resulting in higher abundance and diversity, which enabled functional stability under varying environmental pressures. In contrast, deterministic processes dominated fungal communities, which exhibited a strong dependence on environmental conditions, making fungi more sensitive to environmental changes and resulting in significant alterations in functional abundance. This study enhances our understanding of soil microbial biogeography, highlighting the influence of multiple environmental factors on the spatial distribution of Stipa rhizosphere microbial communities across different scales.