Carbon and nitrogen stable isotope variations in leaves of two grapevine cultivars (Chasselas and Pinot noir): Implications for ecophysiological studies

Abstract

We investigated the within- and between-leaf variability in the carbon and nitrogen isotope composition (δ13C and δ15N) and total nitrogen (TN) content in two grapevine cultivars (Vitis vinifera cv. Chasselas and Pinot noir) field-grown under rain-fed conditions. The within-leaf variability was studied in discs sampled from base-to-tip and left and right regions from the margin to midrib. The intra- and interplant variability was studied by comparing leaves at different positions along the shoot (basal, median, apical). In leaves from both cultivars, a decrease in δ13C from base to tip was observed, which is in line with an upward gradient of stomatal density and chlorophyll concentration. Less important, but still significant differences were observed between the right and left discs. The leaf TN and δ15N values differed between cultivars, showed smaller variations than the δ13C values, and no systematic spatial trends. The intraleaf variations in δ13C, δ15N, and TN suggest that stomatal behavior, CO2 fixation, chlorophyll concentrations, and the chemical composition of leaf components were heterogeneous in the leaves. At the canopy scale, the apical leaves had less 13C and more 15N and TN than the basal leaves, indicating differences in their photosynthetic capacity and remobilizations from old, senescing leaves to younger leaves. Overall, this study demonstrates patchiness in the δ13C and δ15N values of grapevine leaves and species-specificity of the nitrogen assimilation and 15N fractionation. These findings suggest that care must be taken not to overinterpret foliar δ13C and δ15N values in studies based on fragmented material as markers of physiological and biochemical responses to environmental factors.