Leaf-twig carbon isotope ratio differences in photosynthetic-twig desert shrubs.

Carbon isotope ratios were determined for bulk tissues of both leaves and current season twigs of 29 species of Mohave Desert shrubs. Leaf and twig tissues were found to differ in their carbon isotope ratios, only in those species which had photosynthetic twigs. These data suggest that the twigs of these species operate at lower intercellular CO2 values than leaves, an interpretation which is consistent with available gas-exchange data. An effect of microhabitat was also evident between the mean isotope ratios of leaves from wash versus slope habitats.