Fine‐scale spatial distribution of orchid mycorrhizal fungi in the soil of host‐rich grasslands

Abstract

Summary Mycorrhizal fungi are essential for the survival of orchid seedlings under natural conditions. The distribution of these fungi in soil can constrain the establishment and resulting spatial arrangement of orchids at the local scale, but the actual extent of occurrence and spatial patterns of orchid mycorrhizal (OrM) fungi in soil remain largely unknown. We addressed the fine‐scale spatial distribution of OrM fungi in two orchid‐rich Mediterranean grasslands by means of high‐throughput sequencing of fungal ITS2 amplicons, obtained from soil samples collected either directly beneath or at a distance from adult Anacamptis morio and Ophrys sphegodes plants. Like ectomycorrhizal and arbuscular mycobionts, OrM fungi (tulasnelloid, ceratobasidioid, sebacinoid and pezizoid fungi) exhibited significant horizontal spatial autocorrelation in soil. However, OrM fungal read numbers did not correlate with distance from adult orchid plants, and several of these fungi were extremely sporadic or undetected even in the soil samples containing the orchid roots. Orchid mycorrhizal ‘rhizoctonias’ are commonly regarded as unspecialized saprotrophs. The sporadic occurrence of mycobionts of grassland orchids in host‐rich stands questions the view of these mycorrhizal fungi as capable of sustained growth in soil.

Mycorrhizal fungi affect orchid distribution and population dynamics

“…NGS studies have needed multiple sets of primers, with correspondingly higher sequencing costs, to consistently detect OMFs in soil (e.g. Oja et al, 2016;Voyron et al, 2017). Furthermore, because of primer biases and varying copy numbers of ribosomal genes, it is not currently possible to interpret NGS metabarcode data as reflecting abundance.…”

Molecular and Microbiological Insights on the Enrichment Procedures for the Isolation of Petroleum Degrading Bacteria and Fungi

“…In the first PCR, the nr ITS (ITS1-5.8S-ITS2) was amplified with universal primers ITS1F-ITS4 ( White et al, 1990 ). For the second PCR, ITS3 and ITS4 ( White et al, 1990 ) tagged primers were used to amplify the ITS2 region of each DNA sample ( Voyron et al, 2017 ).…”

Next Generation Sequencing of Ancient Fungal Specimens: The Case of the Saccardo Mycological Herbarium

“…Amplification of the nuclear ribosomal ITS2 region for the Illumina sequencing was carried out using a two-step PCR process. In the first PCR the region of interest was amplified using the universal ITS3/ITS4 primers built on the conserved regions flanking the ITS2 (White et al, 1990), while in the second PCR the products of the first amplification were amplified using ITS3mod/ITS4 tagged primers in order to add different 5 bp identifier tags to distinguish sequences from each specimen (Voyron et al, 2016). In this work 18 different tags were used, FIGURE 1 | Pictures of some representative Peziza samples investigated in this work and their herbarium label.…”

“…mycorrhizal soil fungi (Voyron et al, 2016) as guideline. Forward and reverse reads from each library were merged using PEAR v0.9.10 (Zhang et al, 2014) with the quality score threshold set at 28, the minimum length of reads after trimming set at 150 bp and the minimum overlap size set at 100 bp.…”