Spatial structure of fungal DNA assemblages revealed with eDNA metabarcoding in a forest river network in western Japan

Growing evidence has revealed high diversity and spatial heterogeneity of fungal communities in local habitats of terrestrial ecosystems. Recently, the analysis of environmental DNA has been undertaken to study the biodiversity of organisms, such as animals and plants, in both aquatic and terrestrial habitats. In the present study, we investigated fungal DNA assemblages and their spatial structure using environmental DNA metabarcoding targeting the internal transcribed spacer 1 (ITS1) region of the rRNA gene cluster in habitats across different branches of rivers in forest landscapes. A total of 1,956 operational taxonomic units (OTUs) were detected. Of these, 770 were assigned as Ascomycota, 177 as Basidiomycota, and 38 as Chytridiomycota. The river water was found to contain functionally diverse OTUs of both aquatic and terrestrial fungi, such as plant decomposers and mycorrhizal fungi. These fungal DNA assemblages were more similar within, rather than between, river branches. In addition, the assemblages were more similar between spatially closer branches. This spatial structuring was significantly associated with geographic distances but not with vegetation of the catchment area and the elevation at the sampling points. Our results imply that information on the terrestrial and aquatic fungal compositions of watersheds, and therefore their spatial structure, can be obtained by investigating the fungal DNA assemblages in river water.