Environmental selection dominates over dispersal limitation in shaping bacterial biogeographic patterns across different soil horizons of the Qinghai-Tibet Plateau

In this study, we investigated soil bacterial communities across three soil horizons of 60 soil profiles along a 3,500 km transect in the Qinghai-Tibet Plateau. We found that soil genetic horizons could be a good scale plate to differentiate bacterial diversity, community structure and network topology along the vertical gradient of soil profiles in Qinghai-Tibet Plateau. The differences exhibited by bacterial communities across soil horizons were largely explained by environmental heterogeneity, rather than spatial isolation. Our results also showed that deterministic processes (mainly variable selection) decreased with deeper soil horizons, while stochastic processes (mainly dispersal limitation) increased from topsoil to subsoil. These findings provide new insight into the microbial vertical distributions in large-scale alpine regions and highlight the vital role of soil genetic horizons in affecting microbial community assembly. The results have implications for understanding pedogenetic pro