Deterministic assembly and centralized networks define the Pinus massoniana rhizosphere mycobiota

The rhizosphere serves as the most active interface for plant-soil microbial interactions. Resource inputs and micro-environmental gradients within this zone are expected to drive the selective recruitment and structural reorganization of fungal communities. However, systematic evidence regarding the divergence patterns and assembly mechanisms between rhizosphere and bulk soil fungal communities in coniferous forests in subtropical area remains limited.

In this study, we collected 44 soil samples (rhizosphere and bulk soil) from Pinus massoniana plantations. Fungal amplicon sequencing was conducted, integrated with indicator taxa analysis, β-diversity comparisons, null model frameworks (Normalized Stochasticity Ratio, NST), and co-occurrence network topological analysis to resolve the fungal communities "composition-assembly-structure" variations across these two microhabitats.

A total of 2,398 fungal ASVs were identified. While the majority of taxa were shared between habitats, the community composition exhibited significant differentiation: the rhizosphere was relatively enriched with Ascomycota and Mortierellomycota, whereas Basidiomycota predominated in the bulk soil. Multiple potential bioindicators were identified for each niche. Although α-diversity indices showed no significant differences between microhabitats, β-diversity revealed a distinct separation in community structure, and with higher inter-sample heterogeneity observed in the rhizosphere. NST analysis indicated that fungal assembly in the rhizosphere was predominantly governed by deterministic processes, while stochastic processes played a more dominant role in the bulk soil. Co-occurrence networks further demonstrated that both microhabitats possessed highly modular structures. However, the bulk soil network was more complex and highly connected, whereas the rhizosphere network was more centralized with a more uneven distribution of nodal connections.

These findings provide comparative evidence for the divergence in fungal community assembly and network organization in subtropical coniferous forests, offering valuable insights for the assessment and management of forest soil health from a microbial perspective.