Effect of short-term salinity on photosynthesis and ion relations in two sugar beet cultivars

A factorial pot experiment was conducted based on randomized complete blocks design in green house condition to investigate the effect of short-term salt stress on leaf photosynthesis and ion relations of two sugar beet cultivars (Madison and 7233-P29). Plants were exposed to 0, 50, 150, 250, and 350 mM salinity (NaCl and CaCl2 in 5:1 molar ratio) for 48 hours. Measurements were done on youngest fully expanded leaves. Salinity caused a significant reduction in stomatal conductance and consequently leaf net photosynthesis in both cultivars. Net photosynthesis of cv 7233-P29 at low level of salinity (50 mM) at 12 h, 24 h and 48 hours after salinity application decreased by 7.4%, 15.1% and 20%, respectively, compared to control. However, reduction in photosynthesis at highest level of salinity (350 mM) at the same times were 62.4%, 73%, and 72.3%, respectively, compared to control. For Madison the percent of reduction was significantly higher than P29. Cultivar P29 at 12 and 24 hours after salinization had significantly higher Na content than Madison up to 250 mM. Potassium concentration tended to decrease with increase in salinity. Salinity led to increased Cl- concentration in both cultivars. However, Madison had significantly higher Cl- content than P29 at the highest level of salinity at all three times of sampling. A strong correlation between photosynthesis and stomatal conductance (R2=0.98) and weak correlation between photosynthesis and sodium concentration (R2= 0.22), and photosynthesis and chloride concentration (R2=0.55) indicated that in short-term exposure to salinity, stomatal conductance was one of the main causes of photosynthesis.