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 the putative ErM fungal community 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 the ErM fungal community. Moreover, the degree of network specialization in Rhododendron-ErM fungi interactions increased with elevation. Our study provides one of the first investigations into the drivers of ErM fungal community 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.