Genotypic variation of gas exchange parameters and carbon isotope discrimination in winter wheat

Carbon isotope discrimination (Delta) has been suggested as an indirect selection tool for plant water use efficiency and yield potential in wheat (Triticum aestivum L.). Plant available soil water content (PASW) and vapor pressure deficit (VPD) are among some important factors affecting gas exchange and Delta. A two-year field experiment was conducted to (1) investigate the differences in gas exchange parameters: net CO2 assimilation rate (An), stomatal conductance (Gs), intercellular CO2 concentration (Ci), An/Ci, transpiration rate (E), water use efficiency (WUE), and Delta between older and newer cultivars in winter wheat; and (2) determine the relationships between Delta and gas exchange parameters, WUE and grain yield as influenced by PASW and VPD. Differences in An and An/Ci between the two years was influenced more by PASW conditions than by cultivar. In general, WUE decreased in all cultivars when PASW <50 %. There were no correlations between gas exchange parameters, WUE, and grain yield under water stress. In the wetter growing season, the two older cultivars had higher WUE than the two newer cultivars. There was a negative correlation between Delta and WUE with older cultivars tending to have a lower Delta and higher WUE than the newer cultivars. A positive correlation between Delta and grain yield suggests that A values can be used as a supplementary selection tool for higher yielding winter wheat cultivars.