Environmental DNA reveals differential geologic isolation effects on plant and fungal Communities in the Hengduan Mountains

Species range limits are typically constrained by their tolerance to abiotic factors such as climate, as well as by dispersal limitations due to geographic barriers like mountain ridges and river valleys. Montane regions, which are hyperdiverse in many different clades, characterised by high turnover, and complex topography, provide ideal systems for investigating the drivers of range limits. In this study, we collected 30 environmental DNA (eDNA) samples from the tributaries of the Salween, Mekong, and Yangtze rivers in west China and employed ITS2 primers to analyse the species phylogenetic beta diversity of plant and fungal communities. We then applied a null model approach to disentangle the dispersal limitation process from the climate filtering process. Habitat preference analyses indicate that our eDNA samples predominantly capture mid-to-low elevation species. The spatial pattern of the PCoA plot from phylogenetic beta diversity revealed congruent distribution patterns between plant and fungal groups, with assemblage segregation across different river valleys and along latitudes. The plant communities were structured along the Salween-Mekong divide once climatic and distance effects were accounted for. Our results highlight the efficiency of using river eDNA to detect the terrestrial plant and fungi communities and emphasize the dispersal barrier is taxa and location dependent.