Effect of Salinity on Carbon Isotope Discrimination of Shoot and Root of Four Sugar Beet (Beta vulgaris L.) Cultivars

A factorial pot experiment based on randomized complete blocks design with four replications was carried out in order to evaluate salt tolerance of four sugar beet cultivars including Madison (British origin) and three Iranian cultivars (۷۲۳۳-P۱۲, ۷۲۳۳-P۲۱ and ۷۲۳۳-P۲۹) using carbon isotope discrimination (Δ). Plants were grown in sand culture medium in greenhouse conditions. Sugar beet cultivars were irrigated with saline water (tap water as control, ۵۰, ۱۵۰, ۲۵۰ and ۳۵۰ mM of NaCl and CaCl۲ in ۵: ۱ molar ratio) from ۴-leaf stage for ۱۶ weeks. Carbon isotope discrimination significantly decreased with increasing salinity. Significant differences of Δ between shoot and root were observed in all cultivars and all levels of salinity. Madison cv. showed lower Δ in shoot and root than the other three cultivars at all levels of salinity except the control, but cv. ۷۲۳۳-P۲۹ had significantly higher Δ values at saline conditions of ۱۵۰ mM and above. Although the regression of Δ and Ci/Ca was positive, the slope of regression line was different from the pattern predicted by theory, indicating an underestimation of Δ in these samples. Relatively higher ۱۳C (lower Δ) was found in root as compared with shoots.