Environmental changes drive soil microbial community assembly across arid alpine grasslands on the Qinghai-Tibetan Plateau, China

Soil microbes play a key role in regulating ecosystem functions in arid alpine grasslands, which are extremely sensitive to environmental changes. However, the exact mechanism by which multiple environmental factors interact to shape local soil microbial community assembly is unclear. Therefore, exploring how changing environmental factors affect microbial community assembly responds to will help us predict microbial-mediated ecosystem processes under climate change. Here, we conducted large-scale field sampling from 30 alpine grassland sites (e.g., alpine meadow (AM), alpine steppe (AS) and alpine desert steppe (ADS)) across arid ecosystems on the Qinghai-Tibetan Plateau (QTP), China. Soil bacterial and fungal community assembly and their relationships with spatial, climatic, and vegetation-soil factors were studied with the Molecular Ecological Network Analysis Pipeline (MENAP), analysis of variance (ANOVA), canonical correspondence analysis (CCA) and structural equation models (SEMs). The results showed that the soil microbial diversity and co-occurrence network complexity increased significantly from ADS to AS and AM, and bacteria were more susceptible to environmental factors than fungi. The relative abundances of the dominant bacterial phyla, including Acidobacteria, Proteobacteria, Actinobacteria and Gemmatimonadetes, showed a statistically significant increase, while the relative abundance of the fungal phyla Basidiomycota and Glomeromycota showed significant differences across arid alpine grasslands. Variation partitioning analysis (VPA) revealed that vegetation-soil factors contributed the most to explaining the bacterial community composition, whereas spatial factors contributed the most to explaining the variation in the fungal community composition. The results obtained from the SEMs suggested that latitude and soil pH had the greatest impact on the diversity of bacteria and fungi, respectively. Taken together, the results of this study provide a comprehensive perspective on how the soil microbial communities respond to changes in environmental factors across arid alpine grasslands on the QTP, China.