Correlations between Carbon Isotope Discrimination and Leaf Conductance to Water Vapor in Common Beans

Abstract

Carbon isotope discrimination (.DELTA.) was measured in the field on 10 cultivars of common bean (Phasolus vulgaris L.). There was substantial variation (more than 2 .permill..) in leaf .DELTA. values and these differences were maintained between vegetative and reproductive developmental stages. These mean lines also exhibited substantial differences in leaf conductance to water vapor, and again these differences were maintained across developmental stages. The differences in lead conductance were positively correlated with .DELTA. values, whether conductance was measured as total leaf conductance or as the individual conductances of either upper or lower leaf surfaces. The observed differences in leaf conductances were not associated with difference in stomatal density. There were small differences among bean lines in their leaf Kjeldahl nitrogen contents, which is interpreted as indicating that photosynthetic capacity among bean lines was similar. Thus, because .DELTA. values and leaf conductance were positively correlated, these data suggested that there may have been differences among bean lines in the extent to which stomata limited phostosynthetic gas exchnage rates.