| The toxicity of Cu to the seedlings 16 vegetable varieties commonly cultivated and consumed in Fujian Province were studied by water culture to select the most sensitive vegetable to Cu toxicity. This highly sensitive vegetable was cultivated by soil culture to study the effects of Cu on its physiological characteristics and growth. The toxicity threshold of the soil Cu to the highly sensitive vegetable was estimated. The main results were as follows:1. The results of the water culture showed that Cu toxicity resulted in dwarfism of plant, suppression of old roots, shortness and coarseness of new roots, fewer roots, brownness of root points and yellow of leaves. The root length, root weight and biomass of above-ground parts of the vegetables reduced significantly. The positions poisoned and the extent of toxicity was different for different vegetables. Chinese cabbage was the most sensitive while cowpea was the most tolerant to Cu toxicity among all the vegetables tested.2. Chinese cabbage all dead when >200 mg/kg of Cu was added to the soil and largely stopped to grow when 60～160 mg/kg of Cu was added to the soil. The root length, root weight, the root vitality, plant height and the biomass of Chinese cabbage decreased gradually with the increase of added Cu when 5～60 mg/kg of Cu was added to the soil.3. Cu toxicity resulted in the reduction of chlorophyll, increase in carotenoid, damage of PSⅡand decrease in photosynthesis of Chinese cabbage. When 20 mg/kg of Cu was added to the soil, chlorophyll a decreased significantly. When 40 mg/kg of Cu was added to the soil, photosynthesis decreased significantly.4. Under the stress of Cu, the activities of SOD and POD in the leaves of Chinese cabbage increased, while the concentrations of CAT and MDA increased first and then decreased, which led to the increase in membrane permeability. The activities of SOD and POD significantly increased and the above-ground parts of Chinese cabbage were damaged when 10 mg/kg of Cu was added to the soil. The concentration of MDA in the leaves of Chinese cabbage and electrical conductivity increased significantly which resulted in the over oxidation of membrane lipid and increase in membrane permeability.5. Cu toxicity resulted in the reduction in the concentration of NO3- and the activities of nitrate reducates. When 10 mg/kg of Cu was added to the soil, the concentration of NO3- significantly decreased. When 20 mg/kg of Cu was added to the soil, the activities of nitrate reducates reduced dramatically, which inhibited the metabolism of nitrogen in Chinese cabbage.6. The thresholds of soil Cu for 10% reduction in the biomass of Chinese cabbage was estimated by using the regression equation between the biomass of Chinese cabbage and the soil Cu. The thresholds were 5.64 mg/kg for DTPA-extractable Cu and 47.41 mg/kg for total Cu, respectively. The total Cu threshold value was lower than the 2nd class limit of soil Cu as stipulated by China Soil Environmental Quality Standard (50 mg/kg). When the biomass reduced by 10%, the Cu concentration (FW) in the leaves of Chinese cabbage was 3.48mg/kg, lower than the Cu limit for vegetables (10 mg/kg). These results showed that the Cu toxicity thresholds should used to establish the 2nd class datum of soil environmental quality. |
