Root-associated fungal communities on five distant small islands

Root-associated fungi can influence plant germination, growth, survival, reproduction and coexistence. Yet, their diversity and distribution are still poorly known with most studies focusing on single plant species. We studied the diversity, composition and biogeographic patterns of root-associated fungi from small islands of five archipelagos, spanning diverse climates, plant communities and island characteristics. Our results revealed a distinct biogeographic pattern, with minimal taxon overlap and different diversity levels linked to island age, climate, and plant diversity. Ascomycetes dominated all sites, but basidiomycete abundance peaked on tropical islands. Saprotrophs and pathogens were the most abundant functional groups across islands. In contrast, mutualistic fungi showed disproportionately high diversity relative to their low abundance, reaching maximum values on tropical Fregate and temperate Na Redona. Our data also confirm the worldwide distribution of some wind-dispersed ascomycete genera with broad ecological niches, while uncovering unexpected hotspots of wild reservoirs for key plant pathogens.