Abstract: Alpine meadows in Sanjiangyuan (SJY) National Park are experiencing degradation, and soil microbes play a critical role in maintaining the health and stability of these ecosystems. Soil microbes showed strong habitat specificity during meadow degradation, but we poorly understood the ecological assembly processes in soil microbial communities. This study explores the changes in ecological components across original and degraded patches of alpine meadows in SJY National Park. We examined vegetation-soil characteristics through field surveys, and soil microbial community structure by using high-throughput sequencing techniques. At the macro level, alpine meadows degradation increased vegetation species diversity, significantly reduced above-ground productivity, and made the soil more barren and alkaline. At the micro level, although the dominant phyla of soil microorganisms were similar in different degradation states of alpine meadows, degradation significantly increased the relative abundance of oligotrophic bacteria and decreased the relative abundance of dominant fungi. Additionally, microbial communities exhibited significant β-diversity. Degradation also led to an increase in microbial α-diversity, heightened microbial taxa competition, and a more complex microbial co-occurrence network. However, vegetation-soil variables explained only a small portion of the variation in soil microbes. Through the study of microbial ecological assembly processes, it was found that degradation enhanced the stochastic processes of soil microbial communities, and the changes in soil microbial communities were mainly driven by the variations inherent in the microbes themselves. These findings highlight the complex ecological interactions between above- and below-ground components, and emphasize the critical role of microbial community dynamics in ecosystem functions.

Key words: Sanjiangyuan National Park, original patches, degraded patches, soil microbial community structure, microbial community assembly processes