The majority of orchids are found in habitats where light may be a limiting factor. In such habitats it is not surprising that many achlorophyllous (lacking chlorophyll), as well as green, orchids depend on specific mycorrhizal fungal symbionts to supply them with carbohydrates in order to grow. However, orchids are found in a wide range of habitats and range in their photosynthetic capabilities. For those orchids that are fully photosynthetic, and presumably capable of acquiring their own organic carbon, are they less reliant on a specific suite of mycorrhizal fungi? A new study that examines fungal diversity in orchids in open sunny habitats, questions this assumption.
Mariangela Girlanda and Silvia Perotto, from the University of Turin, Italy, whose main areas of research include the biodiversity, phylogeny, and ecology of microfungi, and their colleagues were interested in determining whether the mycorrhizal fungi associated with Mediterranean orchids found in sunny meadow habitats were more diverse and more specific to their orchid partners than previously assumed. They published their results in the July issue of the American Journal of Botany (http://www.amjbot.org/content/98/7/1148.full).
"Earlier studies showed how orchids with little or no photosynthesis gain the organic carbon they need for growth through specific associations with ectomycorrhizal fungi, capable of fetching carbon mainly through symbiosis with other photosynthetic plants or with saprotrophic fungi, breaking down and assimilating complex organic substrates," said Perotto. "A logical hypothesis based on these findings was that fully photosynthetic orchids should not depend on their mycorrhizal partners for organic carbon.
"By contrast, they are expected to transfer to the fungal symbionts part of the photosynthate, like plants normally do," Perotto continued. "This could relax the need for
|Contact: Richard Hund|
American Journal of Botany