AUTHOR=Jacquemyn Hans , Brys Rein , Waud Michael , Evans Alexandra , Figura Tomáš , Selosse Marc-André 

TITLE=Mycorrhizal Communities and Isotope Signatures in Two Partially Mycoheterotrophic Orchids

JOURNAL=Frontiers in Plant Science

VOLUME=Volume 12 - 2021

YEAR=2021

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2021.618140

DOI=10.3389/fpls.2021.618140

ISSN=1664-462X

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 (the autotrophic Platanthera chlorantha, the partially mycoheterotrophic Epipactis helleborine and E. neglecta and the fully 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 the trophic types. Mycorrhizal communities associating with partially mycoheterotrophic orchids consisted of a wide range of fungi belonging to different families, whereas autotrophic and fully mycoheterotrophic species 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 form mycorrhizas with a wide diversity of fungi from different fungal families, but variation in mycorrhizal community composition did not translate into significantly different isotope signatures and thus different transfer of C and N to the plant. We conclude that differences in isotope signatures between E. helleborine and E. neglecta more likely reflect inherent physiological differences than different mycorrhizal communities.