Environmental Driving Mechanism and Response of Soil’s Fungal Functional Structure to Near-Naturalization in a Warm Temperate Plantation

In this study, the near-naturalization process of Pinus tabulaeformis plantations in Baxianshan National Nature Reserve was divided into three stages depending on the proportion of P. tabulaeformis present, resulting in the following categories: the P. tabulaeformis forest stage, the mixed forest stage, and the near-natural forest stage. Natural secondary forests were selected as a control. We assessed alterations in the soil’s fungal functional structures from three aspects: functional mode, vegetative mode, and growth mode, and their responses to vegetation and soil factors were also explored. The results showed that ectomycorrhizal, saprophytic, and plant pathogen types were dominant in the functional mode, and plant pathogens were most abundant in the P. tabulaeformis forest stage. Meanwhile, ectomycorrhizal fungi were the least abundant in the near-natural forest stage. In the vegetative mode, saprophytic, pathophysiological, and symbiotic types were dominant, and pathophysiological types were the most abundant in the P. tabulaeformis forest stage. In the growth mode, microfungi dominated, and the abundance of clavarioid decreased with near-naturalization. The degree of variation in functional structure in the three dimensions increased with near-naturalization, but the structure of natural secondary forests converged. The species composition of tree layer obviously affected the abundance and functional structure of fungi in the three modes, among which Quercus mongolia and Carpinus hornbeam were the most significant. The soil’s pH and nitrate content significantly affected the structure of the functional mode, and the soil’s dry matter content and C/N ratio significantly affected the structure of the vegetative mode. In this study, we explored the interaction between the plant community and soil ecological system during the near-naturalization process of plantations in terms of soil fungi functions, further clarifying the role of soil functions in the succession of plant communities and providing a new perspective on the in-depth exploration of ecosystem interactions during the succession of plantations.