Mycorrhizal Communities and Isotope Signatures in Two Partially Mycoheterotrophic Orchids

Abstract

Partial mycoheterotrophy, the ability of plants to obtain carbon from fungi throughout their life cycle in combination with photosynthesis, appears to be more common within the Plant Kingdom than previously anticipated. Recent studies using stable isotope analyses have indicated that isotope signatures in partially mycoheterotrophic plants vary widely among species, but the relative contributions of family- or species-specific characteristics and the identity of the fungal symbionts to the observed differences remain unclear. Here, we investigated in detail mycorrhizal communities and isotopic signatures in four co-occurring terrestrial orchids (Platanthera chlorantha, Epipactis helleborine, E. neglecta and the mycoheterotrophic Neottia nidus-avis). All investigated species were mycorrhizal generalists (i.e., associated with a large number of fungi simultaneously), but mycorrhizal communities differed significantly between species. Mycorrhizal communities associating with the two Epipactis species consisted of a wide range of fungi belonging to different families, whereas P. chlorantha and N. nidus-avis associated mainly with Ceratobasidiaceae and Sebacinaceae species, respectively. Isotopic signatures differed significantly between both Epipactis species, with E. helleborine showing near autotrophic behavior and E. neglecta showing significant enrichment in both carbon and nitrogen. No significant differences in photosynthesis and stomatal conductance were observed between the two partially mycoheterotrophic orchids, despite significant differences in isotopic signatures. Our results demonstrate that partially mycoheterotrophic orchids of the genus Epipactis formed mycorrhizas with a wide diversity of fungi from different fungal families, but variation in mycorrhizal community composition was not related to isotope signatures and thus transfer of C and N to the plant. We conclude that the observed differences in isotope signatures between E. helleborine and E. neglecta cannot solely be explained by differences in mycorrhizal communities, but most likely reflect a combination of inherent physiological differences and differences in mycorrhizal communities.

Progress and Prospects of Mycorrhizal Fungal Diversity in Orchids

“…In the past half-decade ITS3/ITS4OF were frequently used for identifying mycorrhizal fungal communities in orchid roots of terrestrial orchids and the surrounding soils (Jacquemyn et al, 2015a(Jacquemyn et al, , 2017bEsposito et al, 2016;Duffy et al, 2019). Additionally, ITS86F/ITS4 is still used for the detection of mycorrhizal partners of epiphytic orchids (Cevallos et al, 2017(Cevallos et al, , 2018aHerrera et al, 2019b;Izuddin et al, 2019;Jacquemyn et al, 2021).…”

“…Habitats, including macro-and micro-habitats, indirectly affect the coexistence and widespread distribution of orchid species by affecting the composition, structure, and richness of OMF communities (Figure 1). The community composition of OMF associated with the same orchid species distributed in different habitats, different orchids co-occurring in the same habitat, or different individuals of most orchid Frontiers in Plant Science | www.frontiersin.org species in the same habitat can differ to some extent (Martos et al, 2012;Jacquemyn et al, 2014Jacquemyn et al, , 2015aJacquemyn et al, , 2016aJacquemyn et al, , 2021Waud et al, 2017;Pecoraro et al, 2018;Duffy et al, 2019).…”

“…From a microhabitat perspective, sympatric orchids are usually associated with different OMF (Martos et al, 2012;Jacquemyn et al, 2015aJacquemyn et al, , 2016aJacquemyn et al, , 2021Cevallos et al, 2017;Qin et al, 2019). If two or more species are equally dependent on the same available resources, theoretical models predict that they cannot coexist (niche exclusion); indeed, at small-scale, associating with different mycorrhizal fungi facilitates rational division of the niche space resources among cohabiting species by reducing competition and avoiding indirect exploitation due to asymmetrical benefits from shared fungi (Tilman, 1982;Selosse et al, 2004;McCormick and Jacquemyn, 2014;Gerz et al, 2018).…”

Stigmatodactylus sikokianus (Orchidaceae) mainly acquires carbon from decaying litter through association with a specific clade of Serendipitaceae

“…Therefore, the 13 C and 15 N enrichment patterns suggest that S. sikokianus is a nearly fully mycoheterotrophic plant species that obtains nutrients from litter-decaying fungi, although some uncertainties have remained due to limitations of the stable isotopic approach, including differences in fungal identities and plant metabolism (e.g. Suetsugu et al, 2018;Jacquemyn et al, 2021).…”

Mycorrhizal Fungal Partners Remain Constant during a Root Lifecycle of Pleione bulbocodioides (Orchidaceae)

“…Amplicon library of the fungal ITS2-rDNA sequences was constructed using the primer pair ITS86F/ITS4 [33,34]. The primer pair was selected according to previous studies showing the usefulness for recovering a wide range of OMF [35][36][37]. Polymerase Chain Reaction (PCR) amplification, library construction, and sequencing (Illumina Mi-Seq PE-300) were conducted by Allwegene Tec.…”