Abstract
Orchids are known for their vast diversity and dependency on mycorrhizal fungi. Under in situ conditions, the biotic and abiotic factors determining the composition and distribution of orchid mycorrhizal fungi (OMF) communities remain largely unexplored. Therefore in situ experiments are needed to better understand the interactions between orchids and fungi. A seedling-trap experiment was conducted in the Reserva Biológica San Francisco, a well-known biodiversity hotspot located in the Andes of southern Ecuador. The objective was to investigate the effect of orchid species, site, elevation or temporal variation on the assembly and structure of OMF associated with Cyrtochilum retusum and Epidendrum macrum. The OMF community composition was determined using the Illumina MiSeq sequencing of the internal transcribed spacer 2 (ITS2) region. The results exhibited 83 OMF operational taxonomic units belonging to Tulasnellaceae, Ceratobasidiaceae, Serendipitaceae and Atractiellales. It was observed that the composition of the OMF communities was different among orchid species and temporal variation but was not different among sites. The results further support that orchids have a core of keystone OMF that are ubiquitously distributed and stable across temporal change, whereas the majority of these fungi are randomly associated with the plants.
Highlights
In nature, orchids rely on particular interactions with their pollinators and root fungal associates for completing their life cycle (Selosse, 2014)
BLAST analysis of the representative sequences from reconstructed OTUs showed the presence of sequences matching both mycorrhizal and non-mycorrhizal fungi; the latter were not considered in subsequent analyses
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, comprising members of Tulasnellaceae, Ceratobasidiaceae, Serendipitaceae and Atractiellales
Summary
Orchids rely on particular interactions with their pollinators and root fungal associates (i.e., the mycorrhizal fungi) for completing their life cycle (Selosse, 2014). Cevallos et al (2017) and Herrera et al (in press) demonstrated that OMF communities were siteadjusted, consisting of a core of generalists and ubiquitous orchid mycorrhizal fungi-operational taxonomic units (OMFOTUs), 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. In temperate regions, significant differences in OMF communities were reported across orchid species (Esposito et al, 2016) and through temporal variation (Oja et al, 2015) with a core of generalist and overlapped OMF communities
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