Crassulacean acid metabolism influences D/H ratio of leaf wax in succulent plants

This study sought to characterize hydrogen isotopic fractionation during biosynthesis of leaf wax nalkanes in succulent plants capable of crassulacean acid metabolism (CAM). The metabolic and physiological features of CAM represent crucial strategies for survival in hot and dry climates and have been hypothesized to impact hydrogen isotope fractionation. We measured the stable carbon and hydrogen isotopic compositions (dC and dD, respectively) of individual n-alkanes in 20 species of succulent plants from a global collection of the Huntington Botanical Gardens, San Marino, California. Greenhouse conditions and irrigation with water of constant dD value enabled determination of interspecies differences in net D/H fractionation between source water and leaf wax products. Carbon isotope ratios provide constraints on the extent of CAM vs. C3 photosynthesis and indicate a wide range of CAM use, with dC values ranging from 33.01‰ to 18.54‰ (C27–C33 n-alkanes) and 26.66‰ to 17.64‰ (bulk tissue). Despite the controlled growth environment, we observed ca. 90‰ interspecies range in dD values from 193‰ to 107‰. A positive correlation between dCbulk and dDC31 values with R = 0.60 (dCC31 and dDC31 values with R = 0.41) implicates a metabolic isotope effect as the dominant cause of interspecies variation in the hydrogen isotopic composition of leaf wax n-alkanes in CAM-intermediate plants. 2010 Elsevier Ltd. All rights reserved.