Soil pH determines bacterial distribution and assembly processes in natural mountain forests of eastern China

Abstract Aim There have been numerous studies of forest‐soil microbial biogeography, but an integrated view of edaphic factors, plant, climatic factors, and geographic distance in determining the variation of bacterial community and assembly processes remains unclear at large spatial scales. Here, we analysed the factors affecting the biogeographic pattern and assembly processes of soil bacterial communities under 58 tree species in five natural mountain forests. Location Eastern China. Major taxa studied Bacterial communities. Methods Hierarchical partitioning analysis and distance decay models were performed to evaluate the relative contributions of plant phylogeny, environmental, and spatial variables to the composition of bacterial communities. We applied the nearest taxon index (NTI), β‐nearest taxon index (βNTI), and the modified Raup–Crick metric to reveal the mechanisms of bacterial assembly processes. Results We found that plant phylogeny accounted for a significant, but minor, fraction (0.7%) of the variation in composition of bacterial communities. In contrast, soil pH was the primary determinant of bacterial diversity and community composition, independently explaining 68.6 and 69.9% of the variation, respectively. Based on the NTI analysis, bacterial community assembly was more phylogenetically clustered with increasing soil pH. Variable selection was the predominant process explaining bacterial community assembly when differences in soil pH were ≥ 0.83, whereas homogenizing dispersal dominated when differences in soil pH were <0.83. However, there was no significant relationship between plant phylogenetic distance and βNTI. Main conclusions Our findings provide strong evidence that soil pH predominantly determines bacterial distribution and mediates the relative impact of stochasticity and determinism in soil bacterial community assembly. This suggests that climate‐change associated forest soil acidification could have a dramatic impact on soil bacterial diversity, composition, and function.