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. 2018 Nov 16:9:1664.
doi: 10.3389/fpls.2018.01664. eCollection 2018.

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

Stefania Cevallos  1   2 , Stéphane Declerck  1 , Juan Pablo Suárez  2
Affiliations

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

Stefania Cevallos et al. Front Plant Sci. .

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.

Keywords: biotic and abiotic factors; keystone mycorrhizal; mycorrhizal fungi; seedling-trap experiment; temporal variation.

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Figures

FIGURE 1
FIGURE 1
Photo and schematic illustration of the seedling-trap systems. Seedling-traps included polyvinyl chloride cylinder, 10 seedlings, covered with a sun bag adjusted with a rubber band and a paperclip foldback.
FIGURE 2
FIGURE 2
Set-up of a seedling-trap system on a tree branch.
FIGURE 3
FIGURE 3
Frequency distribution of the identified fungal orders of the orchid mycorrhizal fungi identified in association with Cyrtochilum retusum and Epidendrum macrum.
FIGURE 4
FIGURE 4
Rarefaction curves of orchid mycorrhizal fungi OTU (operational taxonomic unit) richness in four treatments of field experiment. T2: transect T2; Q5: transect Q5; C: Cyrtochilum retusum; E: Epidendrum macrum; S1: 1st sampling and S2: 2nd sampling.
FIGURE 5
FIGURE 5
Non-multidimensional scaling (NMDS) plot of orchid mycorrhizal fungal communities associated with Cyrtochilum retusum at T2 (black dots) and Q5 (white squares) sites (stress value = 0.070).
FIGURE 6
FIGURE 6
Non-multidimensional scaling (NMDS) plot of mycorrhizal fungi detected in Cyrtochilum macrum sampled at two colonization times. The black dots correspond to samples obtained from the first sampling (T2CS1 treatment) and the white triangles correspond to the second sampling (T2CS2 treatment), after three months and one year, respectively, of the assay was established (stress value = 0.058).
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