Fungal Communities and Their Environmental Correlates in BSCs Under Sand-Fixing Plantations in Alpine Sandy Land

The fungal communities within biological soil crusts (BSCs) of alpine sandy lands remain poorly understood, particularly regarding their associations with long-term plantation restoration. Four types of sand-fixing plantations (Salix psammophila, Salix cheilophila, Caragana korshinskii, and Populus simonii) in the Gonghe Basin were chosen as study sites, and bare sand, algae crust, and moss crust samples were obtained from each plot. Soil physicochemical properties and extracellular enzyme activities were measured, and the fungal community was characterized by Illumina high-throughput sequencing of the ITS1 region. We systematically examined how key predicted guilds of fungal communities and their environmental factors changed across crust types, and characterized the differentiation of predicted guilds. Our main results are summarized below: (1) Ascomycota and Basidiomycota dominated at the phylum level, while Preussia, Alternaria, Paraphoma, and Endocarpon dominated at the genus level. (2) Moss crust had the highest fungal richness and evenness, followed by algae crust, whereas bare sand had the lowest values. Furthermore, PCoA-ANOSIM further revealed marked differences in BSC fungal community structure among the plantations. (3) Spearman’s correlation analysis, CCA, and the Mantel test indicated that the plantations were associated with fungal community differentiation through variation in edaphic physicochemical properties and extracellular enzymatic activity. Furthermore, pH, AK, and AP were associated with fungal community composition in both crust types, with ALP and SUC additionally important in algae and moss crusts, respectively. (4) FUNGuild predictions indicated that Undefined Saprotroph was the dominant predicted guild and that saprotrophy was the dominant trophic mode in the BSC fungal communities of the study area. This study revealed the fungal community composition and organization of BSCs across various crust types, and identified the factors associated with these communities in different artificial sand-fixing plantations in alpine sandy land. These findings may offer a microbiological foundation for restoring alpine sandy land ecosystems in the future.