Light intensity surpasses soil factors in shaping dynamics and functions of Sophora davidii-associated bacterial communities during forest succession

The rhizosphere is an active zone of plant-microbial interactions influenced by habitat conditions. However, its responses to light intensity and soil nutrients during forest succession remain unclear. Using 16S rRNA gene sequencing, we characterized rhizosphere bacterial communities associated with Sophora davidii (which typifies a leguminous pioneer species crucial for forest succession and ecological restoration on the Loess Plateau of China) compared to bulk soil communities across forest edge and understory habitats, representing early and late successional stages. Rhizosphere communities exhibited significantly lower alpha diversity and diminished stability than bulk soil, particularly in the understory. The taxonomic composition of rhizosphere communities varied across habitats, as exemplified by enrichment of Mycobacteriaceae and Bacillaceae at the forest edge and in the understory, respectively. Unlike bulk soil communities dominated by deterministic assembly, rhizosphere communities balanced deterministic and stochastic processes, with greater stochasticity in the understory. Distinctions in community structure were evident between rhizosphere and bulk soil communities due to the influence of soil chemical properties. Still, light intensity emerged as a leading factor in shaping the composition and assembly of rhizosphere communities. Functional predictions revealed that rhizosphere communities were widely involved in nitrogen cycling, with enhanced network robustness and functional differentiation in the understory, reflecting ecological adaptation to successional environments. This study underscores the greater role of light intensity than soil factors in shaping rhizosphere bacterial communities associated with leguminous plants during forest succession, providing insights into plant–microbe–environment interactions and informing ecological restoration strategies.