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

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• 作者：Leho Tedersoo ; Prune Pellet ; Urmas K?ljalg and Marc-André Selosse
• 关键词：Mixotrophy ; Pyroleae ; Stable isotopes ; Ectomycorrhizal fungi ; Ericaceae
• 刊名：Oecologia
• 出版年：2007
• 出版时间：March, 2007
• 年：2007
• 卷：151
• 期：2
• 页码：206-217
• 全文大小：333 KB
• 刊物类别：Biomedical and Life Sciences
• 刊物主题：Life Sciences
  Ecology
  Plant Sciences
  
• 出版者：Springer Berlin / Heidelberg
• ISSN：1432-1939

文摘

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.