Soil pH and moisture govern the assembly processes of abundant and rare bacterial communities in a dryland montane forest.

The assembly mechanisms and ecological drivers of abundant and rare bacterial subcommunities in dryland montane forest ecosystems remain unclear. Here, we compared the biogeographic patterns of rare and abundant bacterial subcommunities and examined the ecological drivers governing their assembly processes in a dryland montane forest of China. Our results showed that a stronger relationship existed between phylogenetic turnover and spatial distance in rare subcommunities compared with that in abundant subcommunities. Null model analysis indicated that abundant subcommunities were predominantly controlled by dispersal limitation, whereas variable selection controlled rare bacterial assembly. More importantly, the balance between deterministic and stochastic processes for abundant and rare subcommunities was regulated by soil pH and soil moisture content, respectively, rather than aridity. Increasing soil moisture decreased the importance of deterministic processes for rare bacterial assembly. In abundant subcommunities, the dominance of stochastic processes was higher in neutral pH soils. Our findings suggested that divergent assembly mechanisms underlying distinct biogeographic patterns in rare and abundant bacterial subcommunities in dryland montane forests, and the assembly mechanisms of abundant and rare bacterial subcommunities were mediated by differentiated environmental factors. Our study provides a new understanding of the generation and maintenance of soil biodiversity in dryland ecosystems.