11 - Carbon and Water Relations in Desert Plants: An Isotopic Perspective

Abstract

This chapter explores the role played by stable isotopes to help understand the water and carbon relations of desert plants from both abiotic and biotic interaction perspectives. Direct extrapolation of carbon isotope discrimination data to water-use efficiency among plants assumes that leaf temperatures are equal. Rarely is this exactly satisfied; leaf temperatures are within several degrees of each other, depending on leaf size, thermal load, and transpiration rate. Plants in aridlands have low carbon isotope discrimination (Δ) values. However, substantial variation in Δ values does exist within plant communities, and it is negatively correlated with the life expectancy of a species. At the population level of a species, high Δ values appear to be associated with high growth rate under noncompetitive conditions, whereas low Δ values appear to be related to the ability to persist through long-term drought conditions. Variation in Δ within a population may be related to selection for either tail of the distribution, driven by both spatial and temporal variability in habitat quality and water availability.