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

Abstract

A factorial pot experiment based on randomized comp lete blocks design with four replications was carried out in order to evaluate s alt tolerance of four sugar beet cultivars including Madison (British origin) and three Irania n cultivars (7233-P 12 , 7233-P 21 and 7233-P 29 ) using carbon isotope discrimination ( ∆ ). Plants were grown in sand culture medium in greenhouse conditions. Sugar beet cultiva rs were irrigated with saline water (tap water as control, 50, 150, 250 and 350 mM of N aCl and CaCl 2 in 5: 1 molar ratio) from 4-leaf stage for 16 weeks. Carbon isotope disc rimination significantly decreased with increasing salinity. Significant differences of ∆ between shoot and root were observed in all cultivars and all levels of salinity. Madison cv. showed lower ∆ in shoot and root than the other three cultivars at all levels of salinity except the control, but cv . 7233-P 29 had significantly higher ∆ values at saline conditions of 150 mM and above. A lthough the regression of ∆ and C i /C a was positive, the slope of regression line was differen t from the pattern predicted by theory, indicating an underest imation of ∆ in these samples. Relatively higher 13 C (lower ∆ ) was found in root as compared with shoots. Keywords : Carbon/ Nitrogen ratio, Photosynthesis, Salt stre ss, Stomatal conductance, Water use efficiency.