Biogeographic and climatic determinants of host-specific phyllosphere fungus-secondary metabolite associations

Phyllosphere microbiomes can modulate leaf-associated secondary metabolites in managed grasslands under biotic and abiotic stress. Yet the ecological drivers linking host plants, phyllosphere fungi, and secondary metabolites in warm-season grasslands remain poorly understood. We surveyed 13 cattle ranches across Florida from 2017 to 2019, profiling leaf-associated fungal communities and targeted secondary metabolites in four perennial warm-season grasses. Fungal assemblages and metabolite composition were significantly structured by geography, climate, and host grass species. Warmer, high-irradiance southern sites harbored greater fungal diversity (particularly among foliar endophytes, mycoparasites, and epiphytes) and metabolite chemodiversity, alongside more complex fungal co-occurrence and fungus-metabolite associations. Host identity further partitioned taxa and metabolites across the landscape, yielding site-dependent association patterns that predicted metabolite composition. Together, these results provide field-based evidence that climate- and host-mediated filtering shapes the linkage between phyllosphere microbes and chemical phenotypes, improving our ability to predict microbiome-driven functional outcomes in grasslands under changing climates. Phyllosphere fungal assemblages and secondary metabolite profiles showed strong biogeographic, climatic, and host-specific patterns, while warmer, high-irradiance sites had greater fungal diversity and more complex fungal and fungus-metabolite associations, based on a survey of 13 cattle ranches in Florida during 2017-2019.