Variation in carbon isotope discrimination in relation to plant performance in a natural population of Cryptantha flava. Oecologia 145:541–548

Abstract 1 Few studies of phenotypic selection have focused on physiological traits, especially in 2 natural populations. The adaptive significance of plant water-use efficiency, the ratio of 3 photosynthesis to water loss through transpiration, has rarely been examined. In this study, 4 carbon isotopic discrimination, , an integrated measure of water-use efficiency, was repeatedly 5 measured in juveniles and adults in a natural population of the herbaceous desert perennial 6 Cryptantha flava over a four-year period and examined for plasticity in , consistency between 7 years in values of , and evidence for selection on phenotypes. There was significan