Orchid–mycorrhizal fungi interactions reveal a duality in their network structure in two European regions differing in climate

Abstract

Network analysis is an effective tool to describe and quantify the ecological interactions between plants and root‐associated fungi. Mycoheterotrophic plants, such as orchids, critically rely on mycorrhizal fungi for nutrients to survive, so investigating the structure of those intimate interactions brings new insights into the plant community assembly and coexistence. So far, there is little consensus on the structure of those interactions, described either as nested (generalist interactions), modular (highly specific interactions) or of both topologies. Biotic factors (e.g., mycorrhizal specificity) were shown to influence the network structure, while there is less evidence of abiotic factor effects. By using next‐generation sequencing of the orchid mycorrhizal fungal (OMF) community associated to with plant individuals belonging to 17 orchid species, we assessed the structure of four orchid–OMF networks in two European regions under contrasting climatic conditions (Mediterranean vs. Continental). Each network contained four to 12 co‐occurring orchid species, including six species shared among the regions. All four networks were both nested and modular, and fungal communities were different between co‐occurring orchid species, despite multiple sharing of fungi across some orchids. Co‐occurring orchid species growing in Mediterranean climate were associated with more dissimilar fungal communities, consistent with a more modular network structure compared to the Continental ones. OMF diversity was comparable among orchid species since most orchids were associated with multiple rarer fungi and with only a few highly dominant ones in the roots. Our results provide useful highlights into potential factors involved in structuring plant–mycorrhizal fungus interactions in different climatic conditions.

Co‐occurring orchid species associated with different low‐abundance mycorrhizal fungi from the soil in a high‐diversity conservation area in Denmark

“…We identified a relatively high number of OMF partners for each orchid species and a considerable overlap in fungal taxa (Figure 4). However, the difference in abundance among OMF strains revealed by the metabarcoding approach suggests that each species is mainly associated with a few OMF OTUs, with the rest found in very low abundance, as reported for a range of terrestrial orchids (Mennicken et al, 2023). This pattern matches the apparent generalism concept suggested by Shefferson et al (2019), in which a species would be specialized towards a few fungi providing unique resources, across habitats, but also associated with other fungi that contribute with functionally redundant resources.…”

Diversity of Mycorrhizal Fungi in Temperate Orchid Species: Comparison of Culture-Dependent and Culture-Independent Methods

“…In May-June 2018, we collected three to five roots per flowering plant from 309 individuals of 19 orchid species located in species-rich mesic grasslands in the Czech Republic, referred to as CZ1 and CZ2 (49 • 7 ′ N, 13 • 39 ′ E and 48 • 53 ′ N, 17 • 31 ′ E), and in southern France, referred to as FR1 and FR2 (43 1). The current study is an extension of the previous sampling focused on the coexistence of orchid communities in species-rich grassland habitats [37]. The four sites had similar soil parameters, though the climatic conditions differed (Mediterranean climate with dry summers vs. continental climate of Central Europe; see details in [37]).…”

“…The current study is an extension of the previous sampling focused on the coexistence of orchid communities in species-rich grassland habitats [37]. The four sites had similar soil parameters, though the climatic conditions differed (Mediterranean climate with dry summers vs. continental climate of Central Europe; see details in [37]). For fungus isolation and identification, roots were transported to the lab in moist plastic bags, placed in the fridge and subjected to both culture-dependent and culture-independent methods in the following days.…”

“…MiSeq Illumina sequencing was conducted by the SEQme Company (Dobříš, Czech Republic). Bioinformatic procedures were applied after (i.e., sequence's merging, quality thresholds, removal of singletons and putative chimeras, alignments) (see [37] for further details). The sequences were first grouped into putative OMF taxa at a similarity of ≥85% if they belonged to the rhizoctonian families (Ceratobasidiaceae, Tulasnellaceae and Serendipitaceae) and thus separated from other ectomycorrhizal and saprotrophic fungi.…”

Fungal community characteristics of the last remaining habitat of three paphiopedilum species in China

“…Moreover, locations close to orchid plant growth represent fungal hotspots for seed germination and new plant establishment. However, most of the current studies have focused on the endophytic fungi and rhizosphere fungal communities of orchids [30][31][32][33] while ignoring the fungal communities in habitat soil. This lack of understanding of the species source and process of orchid mycorrhizal fungal community construction restricts the development of simulated environment construction for ex situ conservation.…”