Oecologia

, Volume 151, Issue 2, pp 206–217

Parallel evolutionary paths to mycoheterotrophy in understorey Ericaceae and Orchidaceae: ecological evidence for mixotrophy in Pyroleae

Authors

  • Leho Tedersoo
    • Institute of Botany and EcologyUniversity of Tartu
  • Prune Pellet
    • Centre d’Ecologie Fonctionnelle et Evolutive (CNRS, UMR 5175)Equipe Interactions Biotiques
  • Urmas Kõljalg
    • Institute of Botany and EcologyUniversity of Tartu
    • Centre d’Ecologie Fonctionnelle et Evolutive (CNRS, UMR 5175)Equipe Interactions Biotiques
Ecophysiology

DOI: 10.1007/s00442-006-0581-2

Cite this article as:
Tedersoo, L., Pellet, P., Kõljalg, U. et al. Oecologia (2007) 151: 206. doi:10.1007/s00442-006-0581-2

Abstract

Several forest understorey achlorophyllous plants, termed mycoheterotrophs (MHs), obtain C from their mycorrhizal fungi. The latter in turn form ectomycorrhizas with trees, the ultimate C source of the entire system. A similar nutritional strategy occurs in some green forest orchids, phylogenetically close to MH species, that gain their C via a combination of MH and photosynthesis (mixotrophy). In orchid evolution, mixotrophy evolved in shaded habitats and preceded MH nutrition. By generalizing and applying this to Ericaceae, we hypothesized that green forest species phylogenetically close to MHs are mixotrophic. Using stable C isotope analysis with fungi, autotrophic, mixotrophic and MH plants as comparisons, we found the first quantitative evidence for substantial fungi-mediated mixotrophy in the Pyroleae, common ericaceous shrubs from boreal forests close to the MH Monotropoideae. Orthilia secunda, Pyrola chlorantha, Pyrola rotundifolia and Chimaphila umbellata acquired between 10.3 and 67.5% of their C from fungi. High N and 15N contents also suggest that Pyroleae nutrition partly rely on fungi. Examination of root fungal internal transcribed spacer sequences at one site revealed that 39 species of mostly endophytic or ectomycorrhizal fungi, including abundant Tricholoma spp., were associated with O. secunda, P. chlorantha and C. umbellata. These fungi, particularly ectomycorrhizal associates, could thus link mixotrophic Pyroleae spp. to surrounding trees, allowing the C flows deduced from isotopic evidence. These data suggest that we need to reconsider ecological roles of understorey plants, which could influence the dynamics and composition of forest communities.

Keywords

MixotrophyPyroleaeStable isotopesEctomycorrhizal fungiEricaceae

Copyright information

© Springer-Verlag 2006