UPTAKE AND ACCUMULATION OF CADMIUM, ZINC AND LEAD BY SOYBEAN (Glycine max L.) AT DIFFERENT Cd, Cd/Zn AND Cd/Pb SUPPLY LEVELS

In this study, growth responses, uptake and accumulation of cadmium (Cd), zinc (Zn) and lead (Pb) by soybean (Glycine max L.) were examined in three hydroponic experiments: experiment 1 included eight Cd supply levels; experiment 2 was conducted with Cd concentrations ranging from 0 to 400 mu mol l(-1) and two Zn concentration levels (100 and 1000 mu mol l(-1)); experiment 3 was conducted with Cd concentrations ranging from 0 to 400 mu mol l(-1) and two Pb concentration levels (100 and 1000 mu mol l(-1)). The results showed that in all three experiments, the dry matter yield of shoots was much higher than that of roots, and both decreased slightly with increasing Cd supply levels with or without other metals. Cd concentrations in the shoots and roots of soybean increased with increasing external Cd supply levels, peaked at 800 mu mol l(-1) in the nutrient solution with 622.6 and 1350.3 mg kg(-1), respectively (experiment 1). Cd concentrations in the shoots and roots of soybean increased at different gradients with increasing Cd supply levels either in complex treatments of Cd/Zn or in complex treatments of Cd/Pb (experiment 2 and experiment 3). Cadmium had a negative effect on Zn or Pb concentrations in the shoots and roots of soybean when the plants were grown at both low Zn or Pb supply levels (100 mu mol l(-1)) and high Zn or Pb supply levels (1000 mu mol l(-1) Zn or Pb concentrations in nutrient solutions had a positive effect on Cd concentrations in different soybean parts at relatively low Cd supply levels, however a negative effect of Zn or Pb on Cd uptake was noticed at relatively high Cd supply levels, and the influence was not always significant. There existed an antagonistic effect between Cd and Zn, in which increasing Zn or Cd content in nutrient solutions may decrease Cd or Zn accumulation in different tissues of soybean. The antagonistic activity was also determined between Cd and Pb at any Cd/Pb complex supply levels.