Impact of plant species identity and island characteristics on phyllosphere fungal community structure in an island ecosystem

Phyllosphere fungi exhibit a wide range of species and play a pivotal role in island ecosystem biodiversity. They bolster plant resilience against diseases and environmental stresses, facilitate the decomposition of organic materials, and enhance nutrient exchange between plants and their surroundings. Despite extensive research on island biogeography pertaining to flora and fauna, the assembly of phyllosphere fungal communities has not been thoroughly explored. This study addresses this gap by employing high-throughput sequencing to examine phyllosphere fungi associated with three island plant species (Messerschmidia argentea, Morinda citrifolia, and Suriana maritima) across 13 islands in the Xisha Islands region. Our findings reveal significant variances in fungal α-diversity and community composition across different islands, plant species, and functional guilds. The variation in fungal α-diversity was notably correlated with the geographical distance from the mainland and a satellite-derived vegetation index, while the Bray-Curtis similarity in fungal communities was primarily influenced by the geographical distance between islands. Stochastic elements, particularly dispersal limitation and drift, were identified as major drivers of fungal community assembly. Furthermore, we observed that island size impacts the distribution of potential keystone species and their co-occurrence patterns within the fungal groups. Intriguingly, host vegetation was found to exert a stronger selective influence on phyllosphere fungi than island characteristics. These results provide valuable insights into the complex ecological interactions and processes governing fungal communities in isolated and unique environmental settings.