Rainfall Drives Differentiation of Plant Rhizosphere Microbial Communities in Two Different Types of Alpine Wetlands: A Perspective Based on a Carbon-Water Coupling Framework

The alpine wetlands of the Qinghai-Tibet Plateau are confronting significant ecological challenges due to drastic shifts in precipitation patterns. Elucidating the response mechanisms of rhizosphere microbial communities in wetland plants to precipitation events is critical to understanding ecosystem resilience. In this study, sandy wetlands at Niaodao and riverine wetlands at Haergai in the Qinghai Lake basin were selected as study sites. Using Poa alpigena rhizosphere and non-rhizosphere soils as the research subjects, metagenomic DNA sequencing combined with environmental factor analysis was employed to compare the microbial community responses before and after a single pulse precipitation event. The results showed that Proteobacteria and Actinobacteria were the dominant phyla in both wetland types (combined relative abundance > 70%). Rainfall induced a differentiated restructuring of soil microbial community composition across different habitats. In rhizosphere soils, rainfall significantly reduced microbial alpha diversity. Co-occurrence network analysis revealed that the rhizosphere community shifted from a competition-coexistence pattern before rainfall to a cooperative adaptation pattern after rainfall, with significant increases in modular cohesion and the proportion of positive correlations. Metagenomic analysis indicated that the number of differentially abundant metabolic pathways in soil microorganisms increased markedly after rainfall, rising to 46 and 40 pathways in the rhizosphere and non-rhizosphere, respectively (compared to 3 and 31 before rainfall), indicating a shift from carbon reserve metabolism to energy-producing metabolism. Total carbon and water content were identified as the core environmental factors jointly regulating community assembly. This study reveals the mechanism by which regional background, precipitation disturbance, and the rhizosphere effect synergistically drive the succession of microbial communities in alpine wetlands, providing a new paradigm for understanding ecosystem adaptation to climate change.