Ericoid mycorrhizal fungal metacommunity facilitates closely related Rhododendron species coexistence

The structural and ecological significance of ericoid mycorrhizal (ErM) fungi is well recognized. Yet, it remains unknown whether the coexistence of ericaceous plants is facilitated by their symbioses with ErM fungi. Here, we use Rhododendron (Ericaceae) as a model to investigate how phylogenetic and functional limiting similarity, or facilitation through ErM fungal metacommunity, influences their co-occurrence in mountain ecosystems. We found Rhododendron species tended to be phylogenetically and functionally clustered across elevations. However, a substantial dissimilarity in the composition of putative ErM fungi was observed among co-occurring hosts within the same community, especially at higher elevations. Host identity played a predominant role in shaping the composition of ErM fungi. Moreover, the degree of network specialization in Rhododendron-ErM fungi interactions increased with elevation. Our study provides one of the first examinations of drivers of ErM fungal composition and network specialization in a species-rich Rhododendron assemblage. Host-symbiont mutualistic interactions in complex landscapes may offer insights into the coexistence of closely related species.