Carbon and nitrogen supply to the underground orchid, Rhizanthella gardneri

Authors

  • Jeremy J. Bougoure,

    1. School of Plant Biology M090, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia
    2. Present address: University of British Columbia, 3333 University Way, Kelowna, BC V1V1V7, Canada
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  • Mark C. Brundrett,

    1. School of Plant Biology M090, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia
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  • Pauline F. Grierson

    1. School of Plant Biology M090, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia
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Author for correspondence:
Jeremy J. Bougoure
Tel: 1 250 807 9556
Email: jeremy.bougoure@ubc.ca

Summary

  • Rhizanthella gardneri is a rare and fully subterranean orchid that is presumably obligately mycoheterotrophic. R. gardneri is thought to be linked via a common mycorrhizal fungus to co-occurring autotrophic shrubs, but there is no experimental evidence to support this supposition.
  • We used compartmentalized microcosms to investigate the R. gardneri tripartite relationship. 13CO2 was applied to foliage of Melaleuca scalena plants and [13C-15N]glycine was fed to the common mycorrhizal fungus, and both sources traced to R. gardneri plants.
  • In our microcosm trial, up to 5% of carbon (C) fed as 13CO2 to the autotrophic shrub was transferred to R. gardneri. R. gardneri also readily acquired soil C and nitrogen (N), where up to 6.2% of C and 22.5% of N fed as labelled glycine to soil was transferred via the fungus to R. gardneri after 240 h.
  • Our study confirms that R. gardneri is mycoheterotrophic and acquires nutrients via mycorrhizal fungus connections from an ectomycorrhizal autotrophic shrub and directly from the soil via the same fungus. This connection with a specific fungus is key to explaining why R. gardneri occurs exclusively under certain Melaleuca species at a very limited number of sites in Western Australia.

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