PARENT SESSION
Oral Session # 46: Evolutionary Ecology I: Plants.
Presiding: P Minchin
Wednesday, August 6. 8:00 AM to 11:30 AM, SITCC Meeting Room 201.
Evolution of photosynthetic pathways in the Orchidaceae: Evidence from stable isotopes and phylogenetic analysis.
Silvera, Katia*,1, 2, Santiago, Louis1, Schuur, Edward1, Williams, Norris1, Whitten, W1, Winter, Klaus2, 1 University of Florida, Gainesville, FL, USA2 Smithsonian Tropical Research Institute, Balboa, Panama, Panama
ABSTRACT- We investigated the carbon stable isotopic composition of orchids from Panama and Costa Rica to determine if photosynthetic carbon assimilation occurs predominantly by C3 or Crassulacean Acid Metabolism (CAM). Carbon isotopic composition of leaf material showed a bimodal distribution with most species exhibiting values near −27, suggesting a C3 pathway, or around −12, suggesting a CAM pathway. Leaf thickness was related to photosynthetic pathway. Thicker leaves often signified a predominantly CAM pathway, whereas thinner leaves were related to C3 photosynthesis. When incorporated into the orchid phylogeny, the distribution of photosynthetic pathways suggests that C3 is the ancestral state and that CAM evolved more than once in the Orchidaceae. This analysis is part of a larger project in which approximately 1600 species will be analyzed from living and preserved specimens for a greater understanding of the evolution of photosynthetic pathways in orchids.
Key words: orchids, photosynthesis, isotope, CAM