Calcium Influences Growth and Leaf Mineral Concentration of Citrus under Saline Conditions

We determined whether the ability of sour orange seedlings to withstand saline irrigation water could be improved by the addition of calcium to the water. Sour orange (Citrus aurantium L.) seedlings were treated for 4 months with a nutrient solution containing either no NaCl, 40 m m NaCI, or 40 m m NaCl plus various concentrations of CaSO 4 , CaCl 2 , or KCl. After 4 months, the NaCl alone reduced root and shoot dry weights by ≈ 30% with no leaf necrosis. Addition of 1, 5, or 7.5 m m CaSO 4 to solutions containing 40 m m NaCl significantly inhibited the NaCl-induced reductions in shoot dry weight. Addition of 7.5 m m CaCl 2 or 7 m m KCl to the NaCl solution reduced leaf Na, but increased Cl to the toxicity level; hence, growth was not improved. The beneficial effect of CaSO 4 was mainly attributed to a reduction in the accumulation of Na and Cl below the toxicity level in the leaves (0.4% and 0.5%, respectively) without a major increase in total dissolved salts. This study demonstrated that the beneficial effect of adding Ca depended on the anion associated with the Ca salt. Calcium sulfate, but not CaCl 2 , was able to overcome the damaging effect of NaCl to sour orange seedlings.