Co-occurring epiphytic orchids have specialized mycorrhizal fungal niches that are also linked to ontogeny

Abstract

Mycorrhizal symbiosis has been related to the coexistence and community assembly of coexisting orchids in few studies despite their obligate dependence on mycorrhizal partners to establish and survive. In hyper-diverse environments like tropical rain forests, coexistence of epiphytic orchids may be facilitated through mycorrhizal fungal specialization. However, information on the role of orchid mycorrhizal fungi (OMF) in niche differentiation and coexistence of epiphytic orchids is still scarce. In this study, we sought to identify the variation in fungal preferences of four co-occurring epiphytic orchids in a tropical rainforest in Costa Rica by addressing the identity and structure of their endophytic fungal and OMF communities across species and life stages. We show that the endophytic fungal communities are formed mainly of previously-recognized OMF taxa, and that the coexisting orchid species display distinct (OMF) communities while keeping a base of shared fungi. We also found that adult plants keep the OMF of the juvenile stage while adding new mycobionts over time, a strategy that may serve as a complementary mechanism to ful ll the nutritional needs associated with reproduction. This study provides evidence for niche partitioning in coexisting tropical epiphytic orchids through the utilization of speci c OMF, and for an aggregation mechanism where adult orchids keep initial fungal mycobionts of the juvenile stage while adding others.

Comprehensive phylogenetic analyses of Orchidaceae using nuclear genes and evolutionary insights into epiphytism

“…Extant epiphytic orchids primarily occur in closed-canopy rainforests with mainly angiosperm trees (Zotz, 2016;Fernández et al, 2023;Spicer and Woods, 2022); such angiosperm rainforests were estimated to have formed approximately 60 Ma (Carvalho et al, 2021) and then dramatically expanded near the PETM (56 Ma) (Jaramillo et al, 2010;Huurdeman et al, 2021). Additionally, previous time estimations showed that some angiosperm groups, for example, Fabaceae and Malvaceae, that contained dominant trees of modern rainforests rapidly diverged approximately at the same time (Cvetkovic et al, 2021;Benton et al, 2022).…”

“…Orchidaceae are crucial ecologically with a global distribution and occupy diverse niches primarily in tropical rainforests, contributing to over one-fifth of the biodiversity in some rainforests (Küper et al, 2004;Huang et al, 2008;Zhang et al, 2015;Givnish et al, 2016;Dewi et al, 2020). Most of the orchids occurring in forests are epiphytes (~20 000 species; ~19 000-21 000 according to different studies) and represent by far the largest group of epiphytic vascular plants (Zotz, 2013;Zotz et al, 2021;Fernández et al, 2023), providing an excellent model for the study of epiphytism.…”

Climate change will likely facilitate invasion of Asian orchid Eulophia graminea into new areas

“…Often this symbiosis is maintained into adulthood, although the OMF that provide for successful germination are not necessarily the same that associate with adult plants (Bayman et al 2016;Phillips et al 2020;Zhang et al 2018). While some OMF have a very broad distribution, on a local scale they are not ubiquitous so that local orchid populations may associate with different sets of fungi that may involve niche and/or spatial segregation (Fernández et al 2023;McCormick et al 2018;Swift et al 2019), although this is not always the case (Suarez et al 2016). The spatial distribution of the fungi may be dependent on biophysical factors which, in turn, would affect the distribution of their orchid symbionts (Izuddin et al 2019;Jacquemyn et al 2016).…”