Abstract: The phyllosphere microbiota greatly affects ecosystem carbon and nitrogen cycles, plant productivity, and stress tolerance. However, the microbial composition and underlying mechanisms in the alpine grassland of Qinghai-Tibetan Plateau (QTP) remain unclear. Here, geographic patterns in the abundance, diversity, and community composition of phyllosphere microbiota and their functions were explored. We found that both phyllosphere bacterial and fungal community composition displayed a geographical dependence. We highlighted the importance of climate, especially mean annual precipitation, in shaping phyllosphere microbial communities at broad geographic scales. The mean annual precipitation explained 4%–34% of the variation in the phyllosphere microbial community. A distinctive feature of the QTP phyllosphere microbiota is the prevalence of positive correlations in microbial co-occurrence networks, contrasting with patterns observed in other ecosystems. Further analysis reveals that ecosystem multifunctionality is strongly associated with microbial abundance and interspecies interactions, with bacterial communities exerting a disproportionately large influence compared to fungi. These findings can cumulatively provide a solid understanding of the patterns and mechanisms of phyllosphere microbial community and function across environmental gradients on the Qinghai-Tibetan Plateau and new perspectives for sustainable alpine grassland management.

Key words: biogeography, phyllosphere microbiota, microbial network, ecosystem multifunctionality, alpine grasslands