Effect of moisture regime on cadmium toxicity in spinach and lettuce

Document Type : Research Paper


1 Persian Gulf and Oman Sea Ecological Research Institute, Iranian fisheries science Research Institute, Agricultural Education and Extension Research Organization, Bandar Abbas, Hormozgan, Iran

2 Soil Science Department, Faculty of Agriculture, Siraz University, Shiraz, Iran

3 Hormozgan Environment, Bandar Abbas, Iran


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.


Main Subjects

Extended Abstract



Heavy metals are added to water and soil along with waste from factories and impose their toxic effects on plants, animals and soil microorganisms. The concentration of heavy metals in natural conditions is relatively low, but due to the addition of industrial waste and pollutants to the environment, it increases significantly. A large part of Iran's agricultural land is located in arid and semi-arid areas. In most dry areas, agriculture is more or less faced with the problem of moisture stress. Undoubtedly, drought is the most important environmental factor affecting growth in semi-arid regions of the world. Considering the lack of water in Iran, investigating the effect of moisture regime on the growth and concentration of cadmium in plants is of particular importance. In this regard, a research was conducted to investigate the effect of cadmium in different humidity conditions on agricultural products, especially leafy vegetables such as lettuce and spinach.


Material and Methods

A greenhouse factorial experiment in the form of a randomized complete block design with three three irrigation intervals (2, 4 and 7 days) and six levels of cadmium (0, 5, 10, 20, 40 and 80 µg g-1soil) in three replicates on the variety Local spinach (Spinosa oleracea) and lettuce (Lactuca sativa) were done. 15 seeds were planted in each pot and the first irrigation was done up to the field capacity and the pots were weighed daily and the humidity was maintained up to the field capacity. For each humidity treatment, the difference in the weight of the pot at the beginning and end of each period was considered as the actual evaporation-transpiration of the pot, and the volume of irrigation water in the desired treatment was calculated for applying the next round. The amount of transpiration was estimated from the difference between evaporation and transpiration. After the end of the growth period (after ten weeks), the leaves and stems were dried in the oven until reaching a constant weight. The concentration of cadmium in the stem and leaves was measured with an atomic absorption device.


Results and Discussion

The results showed that with the increase of cadmium level, the average dry weight of leaves and stems of both studied plants decreased significantly. The average index of sensitivity to moisture stress in lettuce leaves increased significantly with the increase of moisture stress, but in the stem, sensitivity to moisture stress decreased with the increase of moisture stress, but this decrease was not significant. The average of this index increased with the increase of cadmium concentration. So that at each moisture stress level, with the increase of cadmium concentration in the soil, the sensitivity to moisture stress in leaves and stems increased. But the sensitivity to stress was higher in the leaf than in the stem. Increasing irrigation intervals decreased the effect of increasing the cadmium level on the concentration and uptake of cadmium in the plant. With the increase of cadmium level, the rate of evapotranspiration and transpiration decreased significantly. The percentage of reduction of transpiration in 4 and 7 days compared to 2 days in spinach is 41 and 51, respectively, and the percentage of reduction in evaporation and transpiration of spinach in these two irrigation cycles was 33 and 53, respectively.



With the increase irrigation intervals, the concentration and uptake of cadmium in leaves and stems of spinach and lettuce decreased. Considering the positive effect of water on the uptake of cadmium by vegetables, it is recommended to increase the irrigation intervals if these plants are cultivated for nutrition in contaminated soils. In soils with high cadmium contamination, the cultivation of leafy vegetables such as lettuce and spinach is prohibited due to the high uptake power of these plants.


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