Assembly, network stability, and influencing factors of soil bacterial communities along altitudinal gradients in Southwest China’s fragile regions

Human agricultural practices globally impact the composition of soil microbial communities across ecosystems. However, knowledge is limited regarding the structure, composition, stability, assembly processes, and influencing factors of these communities along altitudinal gradients under agricultural disturbance in fragile areas. This study examines bacterial communities in agricultural soils of Camellia oleifera tree plantations along altitudinal gradients in vulnerable regions of Southwest China to examine these aspects. Our findings reveal significant differences in microbial community composition in different altitude zones. Acidobacteriota had the highest proportion in all zones. The highest microbial diversity occurred below 580 m. The complexity and stability of microbial networks peaked between 580 m and 850 m, and the highest network modularity (0.78) occurred above 980 m. Stochastic processes predominantly affected microbial community assembly across altitudinal gradients. Environmental factors and the age of the Camellia oleifera tree stand were dominant factors influencing soil bacterial communities. These findings significantly advance our understanding of microbial community changes in agricultural soils of fragile areas along altitudinal gradients and may provide a scientific basis for managing and improving agricultural soil quality. • The complexity and stability of microbial networks peak between 580 m and 850 m. • Stochastic processes predominantly drive microbial community assembly above 850 m altitude. • Camellia oleifera planting time is an important influence on microbial communities.