15N and 13C natural abundance of autotrophic and myco-heterotrophic orchids provides insight into nitrogen and carbon gain from fungal association

Authors

  • G. Gebauer,

    Corresponding author
    1. Lehrstuhl für Pflanzenökologie, Universität Bayreuth, 95440 Bayreuth, Germany;
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  • M. Meyer

    1. Lehrstuhl für Pflanzenökologie, Universität Bayreuth, 95440 Bayreuth, Germany;
    2. Present address: Lehrstuhl für Physikalische Chemie I, Universität Bayreuth, 95440 Bayreuth, Germany
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Author for correspondence: Gerhard Gebauer Tel: +49 921552060 Fax: +49 921552564 Email: gerhard.gebauer@uni-bayreuth.de

Summary

  • • Whereas mycorrhizal fungi are acknowledged to be the sources of nitrogen (N) and carbon (C) in achlorophyllous (myco-heterotrophic) orchids, the sources of these elements in autotrophic orchids are unknown. We have determined the stable isotope abundance of N and C to quantify their gain from different sources in these two functional groups and in non-orchids of distinctive mycorrhizal types.
  • • Leaves of each plant were collected from four forest and four grassland sites in Europe. The N and C isotope abundance, and total N concentrations of their tissues and of associated soils were determined.
  • • Myco-heterotrophic orchids were significantly more enriched in 15N (ɛMHO-R= 11.5‰) and 13C (ɛMHO-R= 8.4‰) than co-occurring non-orchids. δ15N and δ13C signatures of autotrophic orchids ranged from values typical of non-orchids to those more representative of myco-heterotrophic orchids.
  • • Utilization of fungi-derived N and C probably explains the relative 15N and 13C enrichment in the myco-heterotrophs. A linear two-source isotopic mixing model was used to estimate N and C gain of autotrophic orchids from their fungal associates. Of the putatively autotrophic species, Cephalanthera damasonium obtained the most N and C by the fungal route, but several other species also fell into the partially myco-heterotrophic category.

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