Dual classification reveals diversity patterns and ecological differentiation of foliar endophytic fungi in alpine Rhododendron decorum

The ecological strategies of foliar endophytic fungi in alpine plants remain poorly understood, particularly regarding their niche breadth and spatial distribution. Here, we combined high-throughput sequencing with a dual classification framework based on niche breadth (generalists vs. specialists) and spatial distribution (shared vs. unique taxa) to investigate foliar fungal communities of Rhododendron decorum across five alpine regions in northwestern Yunnan. Foliar fungal communities were consistently dominated by specialists and unique taxa across sites. Niche breadth and spatial distribution were decoupled: 9.5% of specialists were widely distributed across all five sites, whereas 17.9% of generalists were restricted to single locations. Alpha and beta diversity varied geographically and decreased significantly with increasing elevation. Random forest analysis revealed that the key genera driving site differentiation were largely non-overlapping among the four ecological groups, with Phaeosphaeria ranking highest for generalists, Hermetothecium for specialists, Cyphellophora for shared OTUs, and Epicoleosporium for unique OTUs. Co-occurrence network analyses further uncovered distinct structural patterns: specialist networks were more interconnected, generalist networks more modular, shared networks larger and more connected, and unique networks more fragmented with higher modularity and lower clustering. Our dual-classification approach reveals that niche specialization and spatial distribution represent distinct dimensions of fungal ecology. These findings challenge the simplistic view that specialists are necessarily rare or spatially restricted, and underscore the value of integrating both frameworks for understanding microbial community organization in heterogeneous alpine ecosystems.