Assessing the effects of salinity on yield, leaf gas exchange and nutritional quality of spring greenhouse lettuce

摘要

In many coastal areas of the Mediterranean region, vegetable growers are forced to use saline water to irrigate their crops because of the inadequate supply of fresh water. The aim of two greenhouse experiments conducted over two years (2004 and 2005}was to assess the effect of five increasing levels of salinity in irrigation water [0.7 (non-salinized control), 0.9, 1.8, 3.6 or 7.2 dS nr1] on growth, yield, leaf gas exchange and water potential, antioxidant activity, ascorbic acid and nitrate content of spring lettuce [Lactuca sativa L. 'Cambria') grown under a polyethylene shelter. In both years, head diameter and fresh weight as well as the marketable yield decreased linearly as the salinity level in the irrigation water increased. The effect ofthe five levels of salinity on agronomic traits was also reflected at the physiological level. Net C02 assimilation, stomatal conductance and transpiration decreased linearly as the electrical conductivity of the irrigation water increased from 0.7 to 7.2 dS nr1, whereas no significant differences among treatments were observed for water-use efficiency and midday leaf potential. The lowest values of net CO2 assimilation and transpiration were recorded with 7.2 dS nr1, whereas no significant differencesin comparison with the control were recorded between the 0.9 and 1.8 dS m1 treatments. Finally, increasing the electrical conductivity of the irrigation water from 0.7 to 7.2 dS m1 decreased the nitrate content linearly, with the lowest values recorded under severe salt stress conditions (1219 mg kg1 fresh weight).