Controlling factors for soil bacterial and fungal diversity and composition vary with vegetation types in alpine grasslands

Soil microbes have vital functions in terrestrial ecosystems, but the concurrent effects of soil microclimates, edaphic attributes, and plant properties on soil microbial diversity and community composition are rarely evaluated for different vegetation types. Here, we investigated the individual and interactive effects of these controlling factors on soil bacterial and fungal diversity and community composition in alpine meadow and alpine steppe on the Tibetan Plateau. We found that soil microbial diversity and community composition were mainly controlled by edaphic properties, followed by soil microclimates, plant coverage, and root biomass. Also, the dominant regulating effects of the abiotic and biotic factors varied largely with vegetation type. Specifically, soil pH was the main determinant for soil microbes in the alpine meadow, while soil total organic carbon (TOC) played a more important role than other factors for soil microbes in the alpine steppe. The structural equation modeling showed soil moisture (SM) had significant and direct effects on bacterial diversity and community composition in the alpine meadow, and that SM had indirect effects on bacterial diversity in the alpine steppe by positively affecting TOC. Bacterial community composition was mainly influenced by soil pH and TOC, while plant coverage and root biomass were relatively more determinants of fungal community composition. Our findings reveal the key factors controlling microbial diversity and composition in alpine grasslands, which provide insights into the response and adaptation of soil microorganisms to environmental changes and has implications for grassland functioning and management.