The distribution of mycorrhizal fungi on tree barks correlates with the host preference of the tropical epiphytic orchid Bulbophyllum variegatum on La Réunion island

While host preference of tropical epiphytic plants is mainly driven by tree abundance and size, the distribution of mycorrhizal fungi among tree species is likely to influence host preference in orchids. Here, we investigated the host preference of ten epiphytic orchids in a 1-ha forest plot in La Réunion, revealing a strong preference in the orchid Bulbophyllum varigatum. Using an Illumina sequencing of the ITS-2 barcode of fungi, we identified fungal communities, including mycorrhizal Tulasnellaceae, both in the bark of host tree species in the area and in the roots of B. variegatum across the island. Bark-dwelling fungal and mycorrhizal communities varied between tree species, with fungal OTUs being specific to the host of B. variegatum. Three fungi (one Serendipitaceae and two Tulasnellaceae) were found to be mycorrhizal at different stages of the orchid's life cycle. Our results suggest that the uneven distribution of mycorrhizal fungi between tree barks could influence the host preference of epiphytic orchids, a hypothesis that will require experimental testing.