Partial mycoheterotrophy in the green orchid Cypripedium fasciculatum via association with fungi in the Russulaceae and Thelophoraceae.
Whitridge, Henry*,1, Southworth, Darlene1, 1 Southern Oregon University, Ashland, OR, 97520
ABSTRACT- We studied three populations of clustered lady's slipper orchid (Cypripedium fasciculatum) and associated mycorrhizal fungi in southern Oregon. These rare terrestrial orchids are considered a species of concern by several government agencies. Ecological requirements of C. fasciculatum are poorly understood, but it is generally accepted that it maintains mycorrhizal infection into maturity. By analysis of fungal DNA with PCR-RFLP and DNA sequencing, we found that C. fasciculatum associates with several fungal species, at least one in the Russulaceae and one in the Thelephoraceae, both common ectomycorrhizal fungi in coniferous forests. The same fungi were also found in rhizomes of the non-photosynthetic orchid Corallorhiza. Stable isotope analysis of orchid and non-orchid tissues indicates that digestion of fungal biomass in root cells supplies C. fasciculatum with substantial proportions of its carbon and nitrogen. Although C. fasciculatum is green and presumably photosynthetic under favorable conditions, our results indicate that the species also has the ability to parasitize fungi as an intermediate between non-photosynthetic, mycoheterotrophic orchid and non-orchid lifestyles. These results elucidate the ecological connections of C. fasciculatum, and have implications for managing and conserving the species and its accompanying fungi.
Key words: Cypripedium fasciculatum, stable isotopes, mycoheterotrophy, orchid
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