Soil fungal diversity and community assembly: affected by island size or type?

Fungi have a huge biodiversity and play important roles in soil biogeochemical cycling in island ecosystems. Although island biogeography has been widely studied for macroorganisms, fungal community assembly in true islands and its relationship with island area are less documented. We examined soil fungal communities in 18 oceanic islands of two types (eight non-coral islands and 10 coral islands) using the Illumina MiSeq sequencing technique. Our results showed that fungal α-diversity (species richness) was substantially different among the oceanic islands, with a higher value in non-coral islands than in coral islands. Fungal α-diversity was significantly affected by soil potassium and magnesium (Mg) and plant communities in non-coral islands, whereas only soil Mg significantly affected it in coral islands. Soil fungal community composition was significantly different in the non-coral and coral islands and was influenced by soil property, plant community and spatial distance. The ecological stochasticity model showed that the fungal community assembly was mainly governed by deterministic processes regardless of island type. Fungal β-diversity, but not α-diversity, increased significantly with increasing island area. These findings have implications for the better prediction of soil fungal community dynamics in island systems and biodiversity conservation in fragmented habitats.