Carbon and nitrogen isotopic values in Lithops aucampiae during leaf development

Abstract

Lithops (Aizoaceae) are succulent plants consisting of a pair of opposite succulent leaves inserted on an extremely short stem. The apical meristem produces a new leaf pair that develops between the older pair, recycling water and metabolites. This peculiar anatomy and growth form make ecophysiological studies quite challenging. Lithops are considered to have CAM metabolism, though experimental evidence is scarce. We followed the changes in carbon and nitrogen isotopic values in mature leaves, young leaves and roots, with the aim of investigating how the use of resources is optimized to achieve survival in extremely arid environments. Two-year-old plants of Lithops aucampiae were grown in pots with no irrigation for six months. Plants were sampled periodically, and isotopic values were recorded in relation to the developmental pattern of the leaves. δ13C ranged from −16.4 to −13.1‰ with leaves showing less negative values than roots. δ15N ranged between −0.8 and 3.9‰ with leaves showing higher values than roots. To the best of our knowledge, this is the first experimental evidence of carbon and nitrogen isotope values in Lithops, the former providing evidence for CAM metabolism.