Gas Exchange and Chlorophyll Content of Cranberry under Salt Stress

Photosynthetic activity decreases when plants are grown under saline conditions leading to reduced growth and productivity. Leaf gas exchange and chlorophyll content of 'Stevens' cranberry exposed to increasing sodium chloride (NaCl) concentration were measured. Cranberry was grown in a sand based culture under greenhouse conditions. The NaCl concentrations in irrigation water were 0 (control), 82, 164 and 246 mg.L-1. In addition to salt solutions, plants were fertilized with a slow release NPK fertilizer. Intercellular CO2 concentration in leaves increased with increase in salinity (r=0.72, p <= 0.01). Net CO2 assimilation rate decreased by 43%, as exposure rates increased from 0 to 164 mg.L-1NaCl and stomatal conductance relative to the control was reduced by 68% at 164 mg.L-1NaCl. Stomatal conductance had a negative correlation with intercellular CO2 concentration (r=-0.53, p <= 0.1). The ratio of chlorophyll a to chlorophyll b was 1:2 except at 164 mg.L-1NaCl where the ratio was 1:1. The insignificant correlation between stomatal conductance and net CO2 assimilation suggests hat physiological factors other than stomatal conductance were responsible for limiting photosynthesis under salt stress.