Drivers of ectomycorrhizal fungi in a subalpine mixed forest: the roles of host plants and edaphic factors.

Ectomycorrhizal (ECM) fungi are required for most trees in alpine habitats; however, how host identity and edaphic factors influence ECM fungal communities associated with subalpine trees remains poorly known. Here, we collected root tips from four coexisting tree species (Pinus tabuliformis, Picea wilsonii, Populus davidiana, and Betula albosinensis) in a subalpine mixed forest at approximately 2500 m above sea level. We simultaneously characterized the associated ECM fungal communities using Illumina sequencing and analyzed the physicochemical properties of the rhizosphere soil. In total, 254 operational taxonomic units (OTUs) of ECM fungi were identified across all root samples, with the genera Sebacina, Inocybe, Cortinarius, Cenococcum, and Tuber dominating the community. The results revealed high ECM fungal diversity and a notable proportion of OTUs (39%) remained unclassified in the subalpine forest, suggesting the presence of potentially novel fungal taxa. Host identity was a crucial determinant of ECM fungal community composition, structure, and co-occurrence network modularity, reflecting distinct host-specific associations. In addition, soil pH significantly influenced ECM fungal diversity and composition. Collectively, these findings highlight the combined yet asymmetrical roles of host identity and edaphic conditions, especially soil pH, in shaping ECM fungal community in the subalpine forest. These insights underscore the need for further research into the environmental drivers and host associations of ECM fungi across diverse ecosystems, in order to better predict their community dynamics under future environmental change in subalpine regions.