Physiological Responses of Chard and Lettuce to Phosphite Supply in Nutrient Solution

We evaluated the effect of different concentrations of Phosphite (Phi) (0, 0.25, and 0.50 mM) in nutrient solution on lettuce and chard. The fresh and dry biomass of lettuce shoots and heads, root volume, and P accumulation in roots showed no significant differences compared to the controls for different Phi concentrations in nutrient solution. In chard, no statistical differences were found among Phi concentrations for P concentrations in roots and shoots, total free amino-acids in leaves, chlorophyll-b, and soluble sugars. The phosphorus concentration in lettuce shoots was 15.6 and 50.6% higher in plants treated with 0.25 and 0.50 mM of Phi, respectively, compared with the controls. In lettuce, phosphorus levels in roots, total free amino-acids and soluble sugars in leaves were statistically greater for 0.25 mM of Phi in nutrient solution. The concentration of chlorophyll-a, b and total chlorophyll in lettuce leaves increased positively with Phi concentration in nutrient solution. The addition of more than 0.25 mM of Phi to the nutrient solution for chard negatively affected the fresh and dry biomass weight of shoots and roots, and P accumulation in roots and shoots. The concentration of chlorophyll-a, b and total chlorophyll in chard leaves was statistically higher with 0.25 mM of Phi in nutrient solution. We conclude that Phi has differential effects on lettuce and chard physiology, and positive plant responses may be observed when Phi is used up to 0.25 mM in sufficient P conditions.