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.