Abstract
The content of (13)C varies in plants with Crassulacean acid metabolism. Differences up to 3.5 per thousand in the (13)C/(12)C ratios were observed between leaves of different age in the same plant of Bryophyllum daigremontianum. Soluble and insoluble carbon in the same leaf differed up to 8 per thousand, the largest difference occurring in the leaves with the highest Crassulacean acid metabolism activity. Models to account for the isotope discrimination by C(3), C(4), and Crassulacean acid metabolism plants are proposed.