| Chinese cabbage (Brassica campestris L. ssp. Pekinensis) is one of favorite leafy vegetables in China, especially Northern China. There were abundant genotypes available after long-term natural selection and artificial breeding process. However, the pollution of suburb farmland and vegetable field was becoming more and more serious by human's activities. Vegetable plantation on these contaminated soils would significantly threat to human health. Therefore, the selection of Chinese cabbage cultivars with low cadmium(Cd) accumulation in their edible part would be effective approaches to food security. It has been confirmed that the effectiveness of Cd in environment may influence Cd absorption and accumulation in plants. It would thus be beneficial to reduce Cd uptake and accumulation in Chinese cabbage by agronomic practices. In this study, cultivation experiments were carried out to study the Cd tolerance of 21 kinds of Chinese cabbage cultivars. Cultivars with lower uptake and accumulation of Cd would be recommended for the farmers. Meanwhile, greenhouse pot experiment was also conducted to investigate the effect of various fertilization practices on reducing the Cd uptake of the low accumulation Chinese cabbage cultivars. The major results were summarized as follows:1. The results showed that No.6 of the Chinese cabbage cultivar had the highest accumulation potential of Cd under nutrient solution culture. At 0.6mg/kg and 1.0mg/kg Cd levels, the above-ground biomass (dry base) of No.6 was 10.12g/plant and 9.55g/plant, respectively. The corresponding tolerant index was 115% and 103%, respectively. The total amount of accumulated Cd in plants, including the above and under-ground biomass were 3337.16μg/plant for the 0.6 mg/L Cd-treated and 4285.27μg/plant for the 1.0 mg/L Cd treated. All of its indices were the highest of all cultivars. It suggested that No.6 cultivar had great restoration potential for heavy mentals contiminations.2. No.16 and No.21 Chinese cabbage cultivars with low Cd accumulation and high Cd tolerance index were selected out from 21 varieties of Chinese cabbage. The results showed that Cd contents in above-ground shoots of No.16 and No.21 were 171.52mg/kg and 173.53mg/kg respectively at 0.6mg/kg Cd level, whereas it were 219.95mg/kg and 285.73mg/kg respectively at 1.0mg/kg Cd level. All these indices were significantly lower than that of others. Above-ground biomass and the Cd tolerance index of No.16 and No.21 were higher than that of most other varieties, while Cd transportation efficiency was at a low level. Therefore, these two cultivars could be recommended to farmers as low Cd accumulation Chinese cabbage varieties. Combined with rational agronomic measures, No.16 and No.21 could be cultivated in the contaminated soil with a low and middle Cd levels to meet the national food security standards.3. Contents of micro-nutrient-element in shoots and roots of different Chinese cabbage cultivars changed at 0.6mg/kg and 1.0mg/kg Cd concentration. However, the tendency differed between cultivars. For Cd hyperaccumulator No.6, Fe, Mn, Cu and Zn absorptions of above-ground part were inhibited in varying degrees at 1.0mg/kg Cd concentration. However, this kind of response varied among the other cultivars. Cd treatment could restrained Mn absorption of shoots, and promoted Cu absorption of all cultivars'roots and most cultivars'shoots, and also promoted Zn absorption of all cultivars'shoots, except for No.6. These results suggested that there was an antagonistic action between Cd and Mn in shoots, and a synergistic action between Cd and Cu, Cd and Zn in shoots of Chinese cabbage.4. Pot experiment showed that fresh biomass of No.16 increased by 9 and 5 times after the application of manure on the second and third class soils of Cd contamination compared with control treatment. The increasing effect of manure was better than that of calcium magnesium phosphate. Applications of manure and calcium magnesium phosphate could significantly reduce the Cd uptake and reduce Cd content in edible shoots of Chinese cabbage. Compared with the control, manure application reduced Cd contents in shoots by as much as 65% and 42% on the second and third class soils of Cd contamination. The reason was that both manure and calcium magnesium phosphate reduced soil available Cd. Compared with the control, soil available Cd was significantly reduced by 37% with calcium magnesium phosphate application, and 26% with manure application. |
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