Contrasting bacterial and fungal community assembly along an elevational gradient on the Tibetan Plateau: Roles of climate and soil properties

Soil bacterial and fungal communities play critical roles in maintaining ecosystem functions, however, their responses to elevational gradients remain insufficiently understood. In this study, we investigated the diversity, community composition, co-occurrence networks, and assembly processes of soil bacterial and fungal communities along an elevational gradient (5100–5550 m) in the Tibetan Plateau using high-throughput sequencing of 16S rRNA and ITS genes. Bacterial communities were predominantly composed of Pseudomonadota , Bacteroidota and Actinomycetota , whereas fungal communities were primarily composed of Ascomycota , Mucoromycota and Basidiomycota . Bacterial diversity significantly decreased with increasing elevation, while fungal diversity exhibited no clear trend; however, elevation significantly influenced both bacterial and fungal community structures, which were especially associated with climatic variables and soil properties. Co-occurrence network analysis revealed distinct bacterial and fungal network structures, whereas the topology of bacterial–fungal inter-kingdom subnetworks varied non-monotonically among elevations. Null model analysis revealed that bacterial community assembly varied among elevations, with deterministic processes predominating at DGJ3 (5350 m) and DGJ4 (5450 m), whereas stochastic processes dominated at DGJ1 (5100 m), DGJ2 (5250 m), and DGJ5 (5550 m). In contrast, fungal community assembly remained predominantly stochastic along the elevational gradient. Linear regression and structural equation modelling further revealed that climatic factors and soil properties jointly regulated microbial community assembly processes. Overall, climatic and soil factors jointly regulate elevational diversity patterns, community structure, co-occurrence networks, and assembly processes of soil microorganisms, with distinct responses observed between bacterial and fungal communities.