Soil Fungal Community Diversity, Co-Occurrence Networks, and Assembly Processes under Diverse Forest Ecosystems

Fungal communities are critical players in the biogeochemical soil processes of forest ecosystems. However, the factors driving their diversity and community assembly are still unclear. In the present study, five typical vegetation types of soil fungal communities in Liziping Nature Reserve, China, were investigated using fungal ITS sequences. The results show that the topsoil fungal community is mainly dominated by the phyla Ascomycota, Basidiomycota, and Mortierellomycota. Although there was no significant difference in α diversity (Shannon, Simpson, and Pielou evenness indices) among different forest types, there was a significant difference in β diversity (community composition). This study found that soil pH, soil organic carbon, total nitrogen (TN), total phosphorus (TP), and the total nitrogen/total phosphorus (N/P) ratio are the main environmental factors that affect soil fungal communities. Each forest type has a specific co-occurrence network, indicating that these community structures have significant specificities and complexities. Deciduous evergreen broad-leaved forests as well as deciduous broad-leaved and evergreen broad-leaved mixed forests showed high modularity and average path lengths, indicating their highly modular nature without distinct small-scale characteristics. Furthermore, our findings indicate that the structures of topsoil fungal communities are mainly shaped by stochastic processes, with the diffusion limitation mechanism playing a particularly significant role.