Host filtering overrides simulated climate change: plant species identity shapes phyllosphere fungal communities and putative pathogen proportions in an alpine meadow

Phyllosphere fungal communities play critical ecological roles in plant fitness and nutrient cycling in terrestrial ecosystems. However, the influences of multifactorial climate change on foliar mycobiomes across distinct plant functional groups remain poorly understood. To elucidate this, we used an 11-year field manipulation experiment to assess the impacts of simulated warming (+2.0°C) and altered precipitation (−50%, ambient, and +50%) on foliar fungal α-diversity, β-diversity, and functional guilds across four co-occurring alpine host plants: a forb ( Aster diplostephioides ), a grass ( Elymus nutans ), a legume ( Oxytropis kansuensis ), and a sedge ( Kobresia humilis ), combining ITS1 metabarcoding with compositional bias-corrected modeling (Analysis of Compositions of Microbiomes with Bias Correction 2). We found that host plant species identity acted as the overriding ecological filter, explaining 34.1% of community variation ( P = 0.001 ) and predominantly governing putative pathogen proportions ( P < 0.001 ; forb > grass > sedge > legume). In contrast, climate manipulation impacts were strictly host-dependent: experimental warming significantly elevated fungal OTU richness solely in the legume O. kansuensis ( P = 0.012 ), while restructuring community β-diversity exclusively in O. kansuensis ( R 2 = 0.197 , P = 0.001 ) and the sedge K. humilis ( R 2 = 0.119 , P = 0.004 ). In addition, while precipitation shifts minimally affected broad-scale diversity, both climate factors induced fine-scale taxonomic turnover in specific lineages (notably Aureobasidium , Cladosporium , Vishniacozyma , and Colletotrichum ); crucially, overall guild-level putative pathogen proportions remained resilient against all climate treatments and their interactions ( P > 0.25 ). Our findings suggest that host intrinsic filtering and functional buffering outweigh direct short-term climatic pressures, and emphasize that future alpine foliar disease vulnerability will be predominantly mediated by climate-driven shifts in host plant community dominance rather than direct climatic stimulation of potential pathogens. IMPORTANCE The phyllosphere represents a vital ecological interface where fungal communities dictate plant fitness and ecosystem functi