Soil fungal community data of Baishanzu plot

To begin, the 25-ha BSZ forest plot was divided into 625 grids measuring 20 m × 20 m. Soil sampling took place at the intersections of adjacent grids, resulting in 676 grid intersections, all of which served as soil sampling points. In the second round, approximately 70% (473 out of 676) of the grid intersections were randomly selected for extended sampling. The extended sampling method followed [59]: for these selected grid intersections, one direction out of the eight possible directions (east, west, south, north, southeast, southwest, northwest, and northeast) was randomly chosen as the sampling direction. In this direction, two sampling points were randomly selected at distances of 2, 5, and 8 m. In total, 946 sampling points were obtained using this approach.

Upon collection, soil samples were immediately divided into two parts in the field. One part of the fresh soil was transported to the laboratory and stored at -80 °C for high-throughput sequencing to obtain soil fungal data. The other part was used to measure soil physicochemical properties. Prior to analysis, this part of the soil was processed by removing small stones and fine roots, and then passing it through a 2-mm sieve.