Independent recruitment of saprotrophic fungi as mycorrhizal partners by tropical achlorophyllous orchids

Authors

  • Florent Martos,

    1. Centre d’Ecologie Fonctionnelle et Evolutive (CNRS, UMR 5175), Equipe Interactions Biotiques, 1919 Route de Mende, F–34293 Montpellier cedex 5, France
    2. UMR C53 Peuplements Végétaux et Bioagresseurs en Milieu Tropical, Université de La Réunion, 15 Avenue René Cassin, BP 7151, F–97715 Saint-Denis cedex 9, France
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  • Maguy Dulormne,

    1. Conservatoire Botanique des Antilles Françaises, F–97100 Basse Terre, Guadeloupe, France
    2. EA 926 DYNECAR, Université des Antilles et de la Guyane, BP 592, F–97159 Pointe-à-Pitre, Guadeloupe, France
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  • Thierry Pailler,

    1. UMR C53 Peuplements Végétaux et Bioagresseurs en Milieu Tropical, Université de La Réunion, 15 Avenue René Cassin, BP 7151, F–97715 Saint-Denis cedex 9, France
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  • Paola Bonfante,

    1. Dipartimento di Biologia Vegetale dell’Università, Istituto per la Protezione delle Piante – CNR, Viale Mattioli 25, I–10125 Torino, Italy
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  • Antonella Faccio,

    1. Dipartimento di Biologia Vegetale dell’Università, Istituto per la Protezione delle Piante – CNR, Viale Mattioli 25, I–10125 Torino, Italy
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  • Jacques Fournel,

    1. UMR C53 Peuplements Végétaux et Bioagresseurs en Milieu Tropical, Université de La Réunion, 15 Avenue René Cassin, BP 7151, F–97715 Saint-Denis cedex 9, France
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  • Marie-Pierre Dubois,

    1. Centre d’Ecologie Fonctionnelle et Evolutive (CNRS, UMR 5175), Equipe Interactions Biotiques, 1919 Route de Mende, F–34293 Montpellier cedex 5, France
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  • Marc-André Selosse

    1. Centre d’Ecologie Fonctionnelle et Evolutive (CNRS, UMR 5175), Equipe Interactions Biotiques, 1919 Route de Mende, F–34293 Montpellier cedex 5, France
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Author for correspondence:
Florent Martos
Tel: +262 262 938179
Email: florent.martos@univ-reunion.fr

Summary

  • • Mycoheterotrophic orchids have adapted to shaded forest understory by shifting to achlorophylly and receiving carbon from their mycorrhizal fungi. In temperate forests, they associate in a highly specific way with fungi forming ectomycorrhizas on nearby trees, and exploiting tree photosynthates. However, many rainforests lack ectomycorrhizal fungi, and there is evidence that some tropical Asiatic species associate with saprotrophic fungi.
  • • To investigate this in different geographic and phylogenetic contexts, we identified the mycorrhizal fungi supporting two tropical mycoheterotrophic orchids from Mascarene (Indian Ocean) and Caribbean islands. We tested their possible carbon sources by measuring natural nitrogen (15N) and carbon (13C) abundances.
  • • Saprotrophic basidiomycetes were found: Gastrodia similis associates with a wood-decaying Resinicium (Hymenochaetales); Wullschlaegelia aphylla associates with both litter-decaying Gymnopus and Mycena species, whose rhizomorphs link orchid roots to leaf litter. The 15N and 13C abundances make plausible food chains from dead wood to G. similis and from dead leaves to W. aphylla.
  • • We propose that temperature and moisture in rainforests, but not in most temperate forests, may favour sufficient saprotrophic activity to support development of mycoheterotrophs. By enlarging the spectrum of mycorrhizal fungi and the level of specificity in mycoheterotrophic orchids, this study provides new insights on orchid and mycorrhizal biology in the tropics.

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