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Protocols in ecological and environmental plant physiology


Article << Previous     |     Next >>   Contents Vol 32(5)

Distribution of crassulacean acid metabolism in orchids of Panama: evidence of selection for weak and strong modes

Katia Silvera A C, Louis S. Santiago B, Klaus Winter A

A Smithsonian Tropical Research Institute, P.O. Box 2072, Balboa, Ancón, Republic of Panama.
B Department of Integrative Biology and Center for Stable Isotope Biogeochemistry, 3060 Valley Life Science Building, University of California, Berkeley, CA 94720, USA.
C Corresponding author. Email: katiasilvera@yahoo.com
D This paper originates from a presentation at the IVth International Congress on Crassulacean Acid Metabolism, Tahoe City, California, USA, July–August 2004
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Crassulacean acid metabolism (CAM) is one of three metabolic pathways found in vascular plants for the assimilation of carbon dioxide. In this study, we investigate the occurrence of CAM photosynthesis in 200 native orchid species from Panama and 14 non-native species by carbon isotopic composition (δ13C) and compare these values with nocturnal acid accumulation measured by titration in 173 species. Foliar δ13C showed a bimodal distribution with the majority of species exhibiting values of approximately –28‰ (typically associated with the C3 pathway), or –15‰ (strong CAM). Although thick leaves were related to δ13C values in the CAM range, some thin-leaved orchids were capable of CAM photosynthesis, as demonstrated by acid titration. We also found species with C3 isotopic values and significant acid accumulation at night. Of 128 species with δ13C more negative than –22‰, 42 species showed nocturnal acid accumulation per unit fresh mass characteristic of weakly expressed CAM. These data suggest that among CAM orchids, there may be preferential selection for species to exhibit strong CAM or weak CAM, rather than intermediate metabolism.

Keywords: carbon stable isotope, crassulacean acid metabolism, evolution, Orchidaceae, photosynthesis.

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