Effect of moisture regime on cadmium toxicity in spinach and lettuce

Today, by increasing industrial and agricultural activities and the subsequent increase in pollutants, soil and water pollution has become a serious environmental problem. The increase of pollutants in the soil in the conditions of dry climate and drought stress have adverse effects on the biological indicators. In this study the combined effect of cadmium at six levels (0, 5, 10, 20, 40 and 80 mg kg-1 soil) in the form of cadmium sulfate (CdSO4) and three irrigation intervals (2, 4 and 7 days) as a factorial experiment in the form of a completely random basic design with three replications was investigated on spinach (Spinosa oleracea) and lettuce (Lactuca sativa) in calcareous soil with silty clay texture. The obtained results showed that increasing the concentration of cadmium in the soil caused a significant decrease in the average dry weight of leaves and stems of lettuce and spinach. The average dry weight reduction percentage compared to the control at the highest level of cadmium was observed in lettuce leaves and stems as 63 and 46% and in spinach leaves and stems as 54 and 38%, respectively. Increasing the irrigation intervals decreased the dry weight of lettuce and spinach plants significantly compared to the control. The percentage of mean dry weight reduction in 4 and 7 days irrigation intervals compared to 2 days irrigation interval in lettuce leaf and stem was 23, 41, 31 and 63% and in spinach was 19, 39, 24 and 49%, respectively. The increase in cadmium levels increased the concentration of this element in the stem and leaves of lettuce and spinach plants, and by increasing irrigation intervals, the concentration and uptake of cadmium in the leaves and stems of spinach and lettuce decreased. The results of this research showed that the spinach plant absorb and transport cadmium metal more than the lettuce. The stress sensitivity index showed that the moisture stress has reduced the crop tolerance to cadmium. Based on the decrease in dry weight at different levels of cadmium, it can be said that the stem of two plants is more tolerant to cadmium than the leaf.