Crassulacean Acid Metabolism (CAM) Photosynthesis at Barro Colorado Island, Panama

Crassulacean acid metabolism (CAM) photosynthesis traditionally refers to the ability of plants to fix carbon dioxide (CO2) at night and to close the stomates for most of the day, thereby acquiring carbon at extremely low water cost. CAM is the apotheosis of photosynthetic adaptation to drought. Its functional significance is well documented for succulent species from warm semiarid regions. This chapter focuses on a lesser-known aspect of CAM, namely the taxonomically and functionally diverse CAM flora of the humid tropics, where despite high precipitation, CAM occurs in habitats with periodic water-deficit stress and especially among epiphytes. I introduce the CAM pathway, tabulate species capable of CAM from Barro Colorado Island, and review ecophysiological studies on these species. Attention is drawn to the substantial variation of the CAM phenotype, as in many species the CAM cycle is only weakly expressed and its contribution to carbon gain small.