Soil pH dominates elevational diversity pattern for bacteria in high elevation alkaline soils on the Tibetan Plateau

Although studies of elevational diversity gradient for microbes have attracted considerable attention, the generality of these patterns and their underlying drivers are still poorly understood. Here, we investigated bacterial distribution across a high elevational gradient (4328-5228 m a.s.l.) along the Nyainqêntanglha mountains on the Southwestern Tibetan Plateau. We found a decreasing diversity trend with increasing elevation, with pH contributing most to the diversity variation, followed by elevation and mean annual temperature (MAT). Bacterial community composition differed taxonomically and phylogenetically with elevation. Furthermore, partial Mantel analyzes showed that bacterial community composition was significantly influenced by elevation, pH and MAT. Phylogenetic structure analysis indicated that deterministic processes (related to pH) determined bacterial community assembly along this elevation gradient. Our results reinforce the observed rule that pH is of foremost importance in driving bacterial elevational diversity patterns. We also suggest that absence of tree cover and of human disturbance might be important in allowing an underlying elevational trend to reveal itself. Review of other studies suggests that the trend of decreasing diversity at higher elevations might be generally true above the tree line.