So to what degree are these photosynthetic, sunny meadow orchids dependent on their fungal associates for nutrient acquisition?
To answer this question, the authors used stable isotope analysis to compare isotopically distinguishable fungal-derived carbon and nitrogen in orchid tissue and compared it to that of neighboring non-orchid plants. This technique assesses how much of the organic carbon and nitrogen found in the leaves of the orchids was acquired from their fungal partners.
The authors found that all four orchids had higher N15 compared to their neighbors, indicating that these orchids do depend on their fungal symbionts for a substantial amount of nutrition. Moreover, the orchid with the highest fungal specificity, Orchis purpurea had the highest N15 and C13 gain, and was thus partly dependant on its fungal partners for organic carbon.
"Our paper demonstrates that some fully photosynthetic orchids can still gain organic carbon from their mycorrhizal fungal partners," commented Girlanda. "Of course we would like to investigate this phenomenon further in orchids such as Orchis purpurea in order to understand whether carbon dependency may be related to particular seasons, life stages and growth patterns, or to plant species."
"It seems that there is not such a sharp distinction between photosynthetic and non-photosynthetic orchids, despite the different fungal partners and photoautotrophic capabilities," concluded Perotto. "A flow of organic carbon from the fungus to the plant can also occur in photosynthetic species and likely depends on energy demands by the plant during different life stages."
Perotto and Girlanda indicate that there are still many questions they'd like to pursue, such as learning the source for the fungal-derived carbon found in these orchids as well as the functional roles of the mult
|Contact: Richard Hund|
American Journal of Botany