Cadmium Toxicity Of Brassica Juncea (L.) Coss. And The Effects Of Exogenous Phosphorus On The Plant Cadmium Absorption

Hydroponic experiments were used to study the effects of cadmium (Cd) on the plant growth and cadmium absorption of B. juncea var. foliosa and B. juncea var. multiceps seedlings. The results showed that Cd treatments significantly reduced the dry weight of plants and the chlorophyll contents in leaves, also significantly reduced the net photosynthetic rate, the stomatal conductance and the transpiration rate, but increased the intracellular CO₂ concentration of leaves. The Cd concentrations in plants increased significantly with the increasing of Cd concentrations in the growth medium. Most of Cd absorbed by plants were accumulated in the roots. Cd treatments decreased the concentrations of Mn in plant and Zn ,Fe in shoots. In addition, Cd treatments decreased the soluble protein contents in plant ,and increased the activities of POD and GR in the two plant leaves and the activities of SOD in leaves of B. juncea var. multiceps,but decreased the activities of CAT in the two plant leaves. The contents of MDA in the two plant were significantly increased under 100μM Cd treatment.Soil and hydroponic cultures were conducted to study the effects of phosphorus on the plant growth and cadmium absorption of B.juncea var. foliosa and B. juncea var. multiceps seedlings under cadmium stress. The results of hydroponic culture showed that the application of Pi had no obvious effects on plant growth ,and reduce the Cd content in the shoot but increase the Cd content in the root remarkably of B. juncea var. multiceps under cadmium stress. The Pi content in plants enhanced remarkably.but the concentrations of Zn,Ca,Mg,Mn in the shoot declined remarkably when the amount of Pi application increased.The results of soil culture showed that the application of Pi promoted the germination and increased the biomass of B. juncea var. foliosa and B. juncea var. multiceps. With the amended Pi increased, the content of effective Cd in soils and the concentration of Cd in plants declined significantly,the concentration of Pi in plants also enhanced observably, and the contents of Pi in plant under 1mg kg^-1 Cd treated were higher than those that under 10 mg kg^-1 and50 mg kg^-1 Cd treated.Pot experiments and field experiments were also adopted to study the effects of different soil amendments such as SSP(single superphosphate), pig manure, lime and plant ash on the heavy metal absorbtion by plants and the bioavaibility of metals in soils. The results showed that SSP could decrease the content of heavy metals in plants and the bioavaibility of metals in soils,increase the growth and yield of crop.Pig manure could also increase the growth and yield of crop obviously,and the content of heavy metals in plants declined because of the dilution effect. The effect of lime on decreasing the content of bioavailable heavy metals in soils was the best. However,Large amount of lime amendent could decrease the crop yield. The effect of plant ash on decreasing the content of heavy metals in plants were not obvious.