Neighboring trees regulate the root-associated pathogenic fungi on the host plant in a subtropical forest.

Root-associated fungi and host-specific pathogens are major determinants of species coexistence in forests. Phylogenetically related neighboring trees can strongly affect the fungal community structure of the host plant, which, in turn, will affect the ecological processes. Unfortunately, our understanding of the factors influencing fungal community composition in forests is still limited. In particular, investigation of the relationship between the phytopathogenic fungal community and neighboring trees is incomplete. In the current study, we tested the host specificity of members of the root-associated fungal community collected from seven tree species and determined the influence of neighboring trees and habitat variation on the composition of the phytopathogenic fungal community of the focal plant in a subtropical evergreen forest. Using high-throughput sequencing data with respect to the internal transcribed spacer (ITS) region, we characterized the community composition of the root-associated fungi and found significant differences with respect to fungal groups among the seven tree species. The density of conspecific neighboring trees had a significantly positive influence on the relative abundance of phytopathogens, especially host-specific pathogens, while the heterospecific neighbor density had a significant negative impact on the species richness of host-specific pathogens, as well as phytopathogens. Our work provides evidence that the root-associated phytopathogenic fungi of a host plant depend greatly on the tree neighbors of the host plant.