Functional Plant Biology Functional Plant Biology Society
Plant function and evolutionary biology

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 and Klaus Winter A
+ Author Affiliations
- Author Affiliations

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:

D This paper originates from a presentation at the IVth International Congress on Crassulacean Acid Metabolism, Tahoe City, California, USA, July–August 2004

Functional Plant Biology 32(5) 397-407
Submitted: 3 October 2004  Accepted: 6 January 2005   Published: 27 May 2005


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.


We thank Orquideas Tropicales, Inc. and Dr Gaspar Silvera for permitting the use and abuse of the orchids in the greenhouse. We are grateful to Dr Aurelio Virgo for competent assistance in the laboratory. K.S. acknowledges Dr Robert L. Dressler and Dr Germán Carnevali for discussions and comments on species nomenclature. This work was supported by the Smithsonian Tropical Research Institute, the Andrew W. Mellon Foundation, a Smithsonian Tropical Research Institute Internship to K.S. and a National Science Foundation Fellowship to L.S.S.


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