Soil moisture variation plays an important role in shaping the rhizosphere microbial community assembly of Pinus massoniana

Abstract

In subtropical forest ecosystems, water availability and forest type are important environmental factors influencing soil microbial community structure. However, with the development of conifer–broadleaf mixed plantations, how water availability and forest type interact to influence the rhizosphere microbial community structure and assembly processes, as well as their relative importance, remains uncertain. To address this knowledge gap, we investigated three forest types by measuring the physicochemical properties and extracellular enzyme activities in Pinus massoniana rhizosphere soil and conducting integrated analyses of the microbial community structure and composition. Moreover, we systematically explored the underlying assembly mechanisms. Our results revealed that following the introduction of broadleaf tree species, fungal and bacterial communities responded differently to forest type transition in terms of their structure and composition. The fungal communities comprised primarily Ascomycota (14.43–22.82%) and Basidiomycota (33.88–63.80%), whereas the bacterial communities were dominated by Proteobacteria (28.51–43.01%), Acidobacteriota (23.50–32.48%), and Actinobacteriota (11.65–17.91%). Under the influence of forest type transition and soil moisture content reduction, the rhizosphere microbial interaction networks exhibited more notable small-world properties. Furthermore, stochastic processes governed the assembly of most rhizosphere microbial communities, with the fungal community structure and assembly being driven primarily by moisture variation, whereas bacterial communities were shaped by both forest type and moisture variation. Collectively, our findings demonstrate that, in the context of forest type transition and seasonal variation, changes in soil water content further underscore its environmental filtering role in microbial community assembly. These results provide a scientific basis for plantation managers to increase rhizosphere microbial metabolic activity and enhance soil resource availability.