Stage-Specific Differences in Fungal Community Structure and Functional Potential During Litter Decomposition in a Lava Plateau

Litter-inhabiting fungi drive organic matter mineralization, regulate nutrient cycling, and support ecosystem stability. Understanding their dynamics in unique geological habitats is essential for predicting ecological recovery on volcanic landforms. Using high-throughput ITS sequencing and physicochemical analyses, we investigated litter-inhabiting fungal communities across four stand types on the Jingpo Lake lava plateau—shrub forest (SF), deciduous broad-leaved forest (DB), coniferous and broad-leaved mixed forest (CB), and coniferous forest (CF)—at the early (t1) and late (t2) stages of decomposition. The results showed significant differences in litter physical and chemical properties among forest stand types (p < 0.05). Regarding community composition, Ascomycota and Basidiomycota dominated throughout, and the core genera were primarily unclassified_o__Helotiales, Mortierella, and unclassified_k__Fungi. Alpha diversity analysis showed that DB had the highest Shannon and Pielou-e indices at stage t1, while CB exhibited higher OTUs and Chao1 indices at stage t2. Beta diversity showed that SF communities were significantly separated between the two stages. Co-occurrence networks showed the highest connectivity in CF with pronounced modularity. Notably, LEfSe analysis revealed that DB had the fewest biomarkers, suggesting matrix heterogeneity suppresses single-taxon dominance. Functionally, saprotrophs dominated initially but transitioned toward complex soil saprotroph and endophyte assemblages over time. Redundancy analysis (RDA) identified litter moisture content (LMC) and carbon (C) content as primary drivers, orchestrating a systematic shift in community assembly from “moisture-driven colonization” at t1 to “carbon quality screening” at t2. These findings provide a microecological basis for understanding plant-litter-microorganism coupling mechanisms and guiding ecological restoration in lava plateau ecosystems.