Species turnover dominates rhizosphere bacterial and fungal β-diversity of broad-leaved trees in a temperate natural secondary forest, independent of host mycorrhizal type

Background and aims The maintenance of β-diversity in microbial communities is closely linked to the community assembly processes. However, the relative contributions of different assembly processes to the components of β-diversity, as well as the extent to which host plant mycorrhizal types differentially regulate these processes, remain poorly understood. Methods We investigated 20 broad-leaved tree species from a temperate natural secondary forest in China, examined the root functional traits, soil properties, and β-diversity components and assembly processes of rhizosphere soil microbial communities between arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) species. The following hypotheses were tested: (1) species turnover is the dominant component of microbial β-diversity; and (2) the magnitude of species turnover and the proportion of community assembly processes differ between AM and ECM species. Results Species turnover accounted for more than 90% of the β-diversity in both bacterial and fungal communities, supporting hypothesis 1. Bacterial communities were mainly influenced by deterministic processes (homogeneous selection); whereas fungal communities were largely shaped by stochastic processes (dispersal limitation). Mycorrhizal type had no significant effect on the β-diversity and assembly process, hypothesis 2 was not supported. Soil property variation dominates the selective filtering of bacterial communities, while plant trait variation primarily shapes fungal communities by enhancing stochastic processes, especially dispersal limitation. Conclusions In natural secondary forests, the host rhizosphere imposes similar environmental selection pressures on bacteria and restricts fungal dispersal, thereby driving high species turnover. These findings deepening the understanding of species coexistence within forest communities and the mechanisms that sustain soil biodiversity.