Symbioses: Plant, Animal, and Microbe Interactions
Mccormick, Melissa , Good, Kerry , Whigham, Dennis .
Increased mycoheterotrophy under stress in the native orchid, Goodyera pubescens.
Orchids form obligate associations with mycorrhizal fungi whose role may change through the orchidís life. After germination all protocorms (the life history stage between germination and juvenile) are obligate mycoheterotrophs, at least until developing into photosynthetic seedlings. Orchid protocorms digest pelotons (tight coils of fungal hyphae) to obtain nutrients, including carbon. However, the extent to which mature orchids use fungal carbon is a matter of debate. We hypothesized that the extent to which mature orchids obtained fungal carbon, as opposed to photosynthesis, depends on environmental stress, especially shading or drought. We manipulated shade and drought to determine whether mature plants of Goodyera pubescens shifted from photosynthetic carbon to fungal carbon. We constructed shelters that obstructed 95% of incident light, while allowing rainwater to pass through (shade shelters), and shelters that prevented passage of rainwater, while allowing light to pass through (drought shelters). Shelters covered four mature plants at each of three sites. One leaf from each plant was collected at the time the shelters were applied. We also collected one leaf from each of four unmanipulated control plants at each site. After 6 and 12 weeks, we sampled an additional leaf from each plant and analyzed them for carbon and nitrogen isotopic composition. Photosynthetic and fungal carbon sources have distinct δ13C signatures, so we compared initial and post-manipulation plant δ13C isotopic ratios as a measure of the extent to which these different carbon sources were utilized. We also measured the δ15N isotopic ratio, which also reflects plant utilization of fungi. Drought and shading increased plant utilization of fungal carbon. This suggests that while many mature orchids may utilize little fungal carbon under ideal environmental conditions they still depend on their fungi to survive periods of stress. Increased dependence on fungi as a mechanism to survive stress is important for orchid conservation and for understanding orchid responses to predicted increases in drought frequency and intensity.
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1 - Smithsonian Environmental Research Center, P.O. Box 28, 647 Contees Wharf Rd., Edgewater, MD, 21037, USA
2 - Warren Wilson College, Biology and Environmental Studies , P.O. Box 9000, C.P.O. #8039, Asheville, NC, 28815, USA
carbon isotope discrimination
stable isotopic analysis.
Presentation Type: Poster:Posters for Topics
Location: Hall A/Convention Center
Date: Monday, August 2nd, 2010
Time: 5:30 PM