Are there keystone mycorrhizal fungi associated to tropical epiphytic orchids?

Abstract

In epiphytic orchids, distinctive groups of fungi are involved in the symbiotic association. However, little is known about the factors that determine the mycorrhizal community structure. Here, we analyzed the orchid mycorrhizal fungi communities associated with three sympatric Cymbidieae epiphytic tropical orchids (Cyrtochilum flexuosum, Cyrtochilum myanthum, and Maxillaria calantha) at two sites located within the mountain rainforest of southern Ecuador. To characterize these communities at each orchid population, the ITS2 region was analyzed by Illumina MiSeq technology. Fifty-five mycorrhizal fungi operational taxonomic units (OTUs) putatively attributed to members of Serendipitaceae, Ceratobasidiaceae and Tulasnellaceae were identified. Significant differences in mycorrhizal communities were detected between the three sympatric orchid species as well as among sites/populations. Interestingly, some mycorrhizal OTUs overlapped among orchid populations. Our results suggested that populations of studied epiphytic orchids have site-adjusted mycorrhizal communities structured around keystone fungal species. Interaction with multiple mycorrhizal fungi could favor orchid site occurrence and co-existence among several orchid species.

In situ Orchid Seedling-Trap Experiment Shows Few Keystone and Many Randomly Associated Mycorrhizal Fungal Species During Early Plant Colonization

“…In accordance with previous studies performed in tropical areas ( Kottke et al, 2010 ; Cevallos et al, 2017 ), the present results revealed that epiphytic orchids were associated with a highly diverse group of mycorrhizal fungi (represented by 83 OTUs), comprising members of Tulasnellaceae, Ceratobasidiaceae, Serendipitaceae and Atractiellales. Members of Tulasnellaceae appear to be globally distributed, as they have been frequently reported in association with epiphytic orchids in many forests ( Martos et al, 2012 ; Riofrío et al, 2013 ; Suárez et al, 2016 ; Oberwinkler et al, 2017 ).…”

“…Serendipitaceae was the second most frequent group identified (35%), supporting earlier studies that recognized Serendipitaceae as a persistent orchid partner worldwide ( Suárez et al, 2008 ; Martos et al, 2012 ). In a recent study performed in the same geographical location ( Cevallos et al, 2017 ), fungi putatively assigned to Serendipitaceae were the most frequent taxa identified in association with epiphytic adult orchids of the Cymbidieae tribe. However, here we added a second set of complementary primers (ITS86F/ITS4 combined with ITS3/ITS4) to reduce the biases and reach a more accurate description of fungal communities ( Waud et al, 2014 ).…”

“…The evolutionary history of orchids is considered one of the key factors that shape the structure of the OMF community. With more closely related orchid species, more similar OMF communities are predicted ( Těšitelová et al, 2015 ; Cevallos et al, 2017 ). In co-existence, related orchid species tend to be associated with similar mycorrhizal fungi ( Suárez et al, 2016 ), although the entire OMF community structure could be different ( McCormick and Jacquemyn, 2014 ).…”

“…The development of next-generation sequencing (NGS) technologies (i.e., 454 and Illumina) has further helped to improve the characterization of fungal communities and assess their ecological dynamics ( Cardenas and Tiedje, 2008 ). For instance, Cevallos et al (2017) and Herrera et al (in press) demonstrated that OMF communities were site-adjusted, consisting of a core of generalists and ubiquitous orchid mycorrhizal fungi-operational taxonomic units (OMF-OTUs), considered as keystone species (stable component) plus OTUs identified at specific-site orchid populations (dynamic component). This indicates that the structure of the dynamic component of the OMF communities is determined by local environmental conditions and host’s evolutionary history and that keystone species occur irrespective of the orchid species or site.…”

“…A number of biotic (i.e., orchid species) and abiotic (i.e., site, temporal variation) factors have been reported to impact the structure of OMF communities ( Jacquemyn et al, 2012 ; Ercole et al, 2015 ; Esposito et al, 2016 ; Cevallos et al, 2017 ). However, it is often difficult to generalize the ecological premises to all orchid species or geographic regions, mainly because particular combinations of environmental factors may markedly influence the local OMF community structure ( Peay et al, 2010 ).…”