Arbuscular mycorrhizal fungal communities of a mangrove forest along a salinity gradient on Iriomote Island

Aims Arbuscular mycorrhizal (AM) fungi often occur in mangrove ecosystems, but how different AM fungi interact with mangrove plants is still unclear. Here, we aimed to study the root colonization patterns of AM fungi in two major mangrove tree species, Rhizophora stylosa Griff. and Bruguiera gymnorhiza (L.) Lam., that dominate the estuarine and freshwater sides of an ecotone. Methods We sampled the roots and soils in a mangrove forest on an island in southern Japan and examined the root colonization rates and community compositions of AM fungi using microscopy and high-throughput sequencing of the small subunit (18S) rRNA gene. Results Microscopy revealed AM fungal structures in roots from some individuals of B. gymnorhiza but not of R. stylosa . Molecular analysis detected DNA sequences of Glomeraceae species in roots of both species, but detected those of Acaulosporaceae species only in B. gymnorhiza roots. Glomeraceae species were associated with higher soil electrical conductivity (EC), and Acaulosporaceae species with lower soil EC. The presence/absence of sequences of Acaulosporaceae species was significantly associated with the presence/absence of AM fungal structures (microscopic evidence) in B. gymnorhiza . Conclusions Our results suggest that salinity influences AM fungal community composition in mangrove soils, and that AM fungi such as Acaulosporaceae species form trophic associations with B. gymnorhiza and could help mangrove tree nutrition in saline and low-nutrient environments.