Coarse Woody Debris and Litter Layer Exert Differential Roles in Nursing Soil Fungal Communities Across a Subalpine Forest Successional Series

Coarse woody debris (CWD) and litter are important habitats and nutrient sources for soil fungi. However, the roles of CWD and litter in maintaining soil fungal community composition and function at different successional stages remain unknown. Therefore, we collected soils beneath the CWD and litter from a subalpine forest successional series: shrubs, deciduous broadleaf, broadleaf-conifer mixed, mid-succession coniferous, mature coniferous, and over-mature coniferous forests in the subalpine forest region. The diversity, composition, and functional guilds of the soil fungal communities beneath the CWD and litter layer were analyzed using ITS (Internal Transcribed Spacer) sequencing. The CWD significantly changed the composition and functional guilds of the soil fungal communities in the same successional series. However, there was no significant difference in the soil fungal alpha diversity between the two microhabitats at the same successional stage. Notably, the soil beneath the litter layer had more abundant plant pathogens and mycorrhizal fungi, whereas the soil beneath CWD was enriched mainly with saprotrophic and ectomycorrhizal fungi. The relative abundance of plant pathogens and mycorrhizal fungi was significantly related to the soil pH and the CWD stock. In addition, soil nitrogen, carbon, and the C: N ratio were key driving factors for the taxonomic composition and functional guilds of the soil fungal community. In conclusion, CWD exerts critical functions in nursing soil fungal diversity and maintaining the structure and function of soil fungal community mainly due to CWD decomposes slowly, increases soil heterogeneity, and provides with microhabitats and substrates for fungi in a longer term.