A fine‐scale spatial analysis of fungal communities on tropical tree bark unveils the epiphytic rhizosphere in orchids

Abstract

Approximately 10% of vascular plants are epiphytes and, even though this has long been ignored in past research, can interact with a variety of fungi, including mycorrhizal ones. However, the structure of fungal communities on bark, as well as their relationship with epiphytic plants, is largely unknown.• To fill this gap, we conducted environmental metabarcoding of ITS-2 region to understand the spatial structure of fungal communities of the bark of tropical trees, with a focus on epiphytic orchid mycorrhizal fungi, and tested the influence of root proximity.• For all guilds, including orchid mycorrhizal fungi, fungal communities were more similar when spatially closed on bark, i.e., displayed positive spatial autocorrelation.They also showed distance decay of similarity from epiphytic roots, meaning that their composition on bark increasingly differed, compared to roots, with distance from roots.• We first showed that all the investigated fungal guilds presented a spatial structure at very small scales. This spatial structure was influenced by the roots of epiphytic plants, suggesting the existence of an epiphytic rhizosphere. Finally, we showed that orchid mycorrhizal fungi were aggregated around them, possibly resulting from a reciprocal influence between the mycorrhizal partners.

Compatible and Incompatible Mycorrhizal Fungi With Seeds of Dendrobium Species: The Colonization Process and Effects of Coculture on Germination and Seedling Development

“…Orchids have complex symbioses with fungi throughout their lifespan, and OMFs may have important impacts on the distribution, abundance, and population dynamics of orchid populations, and are particularly important for the key processes, such as seed germination and seedling establishment ( Jacquemyn et al, 2012 ; McCormick et al, 2018 ; Shefferson et al, 2020 ). Orchids recruit OMFs from rhizoctonias that are often considered to live as saprobes in the soil around the roots ( Smith and Read, 2008 ) or on tree bark around epiphytic orchids ( Petrolli et al, 2021 ). The Waiting Room Hypothesis proposed that OMFs were recruited from ancestors that colonized roots as endophytes, and root endophytism in the orchid family was a predisposition for mycorrhizal evolution ( Selosse et al, 2009 , 2021 ).…”

Structure and specialization of mycorrhizal networks in phylogenetically diverse tropical communities

“…These results therefore encourage systematically characterizing the composition of the root mycobiome by targeting both sets of regions. Yet, additional fungal lineages may still not be represented in our dataset, like the Tulasnellaceae, which can form mycorrhizal associations with orchids but often fail to amplify with generalist primers [50,73,74]. This suggests that even two generalist and complementary primer sets might still not be sufficient to retrieve the whole endophytic fungal community.…”

Tree size drives diversity and community structure of microbial communities on the bark of beech (Fagus sylvatica)

“…Studies are often conducted over small spatial scales with small sample sizes (e.g., Leff et al, 2015). Lastly, the focus often lies on only a single group of microorganisms, with bacteria and fungi far outweighing terrestrial algae (Aschenbrenner et al, 2017; Petrolli et al, 2021). Integrative sampling of major microbial contributors over regional or potentially even global scales can help identifying not only the diversity of microorganisms but also potential cooperative and competitive interactions among them.…”