Specialized mycorrhizal association between a partially mycoheterotrophic orchid Oreorchis indica and a Tomentella taxon
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Specialized mycorrhizal association between a partially mycoheterotrophic orchid Oreorchis indica and a Tomentella taxon Kenji Suetsugu1 · Takashi F. Haraguchi2,3 · Akifumi S. Tanabe4 · Ichiro Tayasu2 Received: 22 May 2020 / Accepted: 21 October 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The evolution of full mycoheterotrophy in orchids likely occurs through intermediate stages (i.e., partial mycoheterotrophy or mixotrophy), in which adult plants obtain nutrition through both autotrophy and mycoheterotrophy. However, because of its cryptic manifestation, partial mycoheterotrophy has only been confirmed in slightly more than 20 orchid species. Here, we hypothesized that Oreorchis indica is partially mycoheterotrophic, since (i) Oreorchis is closely related to leafless Corallorhiza, and (ii) it possesses clustered, multi-branched rhizomes that are often found in fully mycoheterotrophic orchids. Accordingly, we investigated the nutritional modes of O. indica in a Japanese subboreal forest by measuring the 13C and 15 N abundances and by community profiling of its mycorrhizal fungi. We found that O. indica mycorrhizal samples (all 12 samples from four individuals) were predominantly colonized by a single OTU of the obligate ectomycorrhizal Tomentella (Thelephoraceae). In addition, the leaves of O. indica were highly enriched in both 13C and 15N compared with those of cooccurring autotrophic plants. It was estimated that O. indica obtained 44.4 ± 6.2% of its carbon from fungal sources. These results strongly suggest that in the Oreorchis-Corallorhiza clade, full mycoheterotrophy evolved after the establishment of partial mycoheterotrophy, rather than through direct shifts from autotrophy. Keywords Calypsoeae · Corallorhiza · Ectomycorrhizal fungi · 13C natural abundance · 15N natural abundance · Mycorrhiza · Orchidaceae · Partial mycoheterotrophy · Tomentella
Introduction Most land plants, from liverworts to angiosperms, form mycorrhizal mutualistic relationships wherein fungal partners receive photosynthetic C from associated plants; in turn, plants receive N, P, or water gathered by the fungal mycelia Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00572-020-00999-z) contains supplementary material, which is available to authorized users. * Kenji Suetsugu [email protected] 1
Department of Biology, Graduate School of Science, Kobe University, Kobe, Hyogo 657‑8501, Japan
2
Research Institute for Humanity and Nature, Kita‑ku, Kyoto 603‑8047, Japan
3
Biodiversity Research Center, Research Institute of Environment, Agriculture and Fisheries, Osaka Prefecture, 10‑4 Koyamotomachi, Osaka 572‑0088 Neyagawa, Japan
4
Graduate School of Life Sciences, Tohoku University, Sendai, Miyagi 980‑8578, Japan
(van der Heijden et al. 2015). However, in some cases, plants also depend on fungi as essential sources of C by reversing the polarity of carbon movement (Leake 1994). Orchids are among the most prevalent of th
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