13C/12C Ratio Changes in Crassulacean Acid Metabolism Plants

Abstract
13C/12C ratios have been found in totally combusted leaves of Crassulacean acid metabolism plants to range from −14 to −33 δ 13C‰ compared with a limestone standard. Crassulacean acid metabolism plants apparently utilize both ribulose-1, 5-diphosphate carboxylase and phosphoenolpyruvate carboxylase to assimilate atmospheric CO2 and, depending on environmental conditions, have 13C/12C ratios indicative of either carboxylase or to any intermediate value. The degree of discrimination against 13C and the resultant 13C/12C ratio from the photosynthetically fixed CO2 is influenced by environmental conditions and is not a specific and fixed characteristic of a Crassulacean acid metabolism plant. Certain Crassulacean acid metabolism plants may shift their ratios as much as 17 δ 13C‰ in specific environments.