Effect of Salinity on Growth and Leaf Photosynthesis of Two Sugar Beet (Beta vulgaris L.) Cultivars

This study investigated the variation between two sugar beet (Beta vulgaris L.) cultivars with respect to growth parameters and photosynthetic rates of individual attached leaves during salinization. Sugar beet plants grown in sand culture were gradually exposed to different levels of salinity (0, 50, 150, 250, and 350 mM, NaCl+CaCl2 in 5:1 ratio). Salt concentrations significantly decreased all growth traits. At the highest level of salinity (350 mM), cv 7233- P29 showed a significantly higher leaf area and total dry matter than Madison after eight weeks of salt treatment commencment. Net photosynthesis (ACO2) and stomatal conductance (gs) were strongly affected by salinity. The Na+ and Cl- concentrations in shoots significantly increased as salt concentration increased. Net photosynthesis (ACO2) was plotted against computed leaf internal CO2 concentration (Ci), and the initial slope of this ACO2-Ci curve was used as a measure of photosynthetic ability. Leaves from plants exposed to 50 mM salinity showed little change in photosynthesis, whereas those treated by high levels of salinity had up to 91.5% inhibition in photosynthetic rates and an increase in CO2 compensation point. Leaf chlorophyll content increased with increasing salinity. Although partial stomatal closure occurred with salinization, reductions in photosynthesis were partly non-stomatal at high levels of salt treatment.