Control Measures And Preliminary Research On The Mechanisms For Phytoremediation Of Zinc,cadmium Contaminated Soil Under Sedum Plumbizincicola-oryza Sativa Rotation System

Pot experiments and field plot trial were conducted to study the effect of different N, P and K levels on plant growth, Zn and Cd uptake, and the mechanisms of nutrients on rhizosphere effect of hyperaccumulator Sedum plumbizincicola. Meanwhile, different phosphate amendments (calcium magnesium phosphate and rock phosphate) were also adopted to explore the agronomic mesure that enhance the Cd and Zn remediation efficiency by Sedum plant and so as to producing low cadmium rice.The results of the orthogonally designed experiment showed that addition of nitrogen fertilizer was the main factor on increasing plant biomass. The treatment of N2P1K0 (200 mg kg-1 N,60 mg kg-1 P, no K) reached the highest dry weight of 31.2 g pot-1, which was 3.15 times of CK (N0P0K0). K application was the main factor of enhancing concentration and uptake of heavy metals especially Cd by Sedum plumbizincicola, shoot Cd concentration in treatments of 160 mg kg-1 K were 28.1% higher than the treatments of no K addition, and the phytoextration efficiency was improved when 60 mg kg-1 P was applied. Combined considering the biomass and total uptake of Zn and Cd by Sedum plumbizincicola, the best treatment was low level N and P, combined with high level K (N1P1K2), the Zn and Cd phytoextraction rate for one season of Sedum plumbizincicola were 11.2 mg kg-1 and 0.12 mg kg-1, respectively.In the rhizosphere experiment, the results showed that the urea mainly as NO3-N form in the soil, and the application of P and K enhanced the transformation to NH4-N. The N, P application combined with K increased the absorption for each other. The TOC concentration in the rhizosphere was higher than bulk soil, and results were the same as NH4OAc-extracted Zn and Cd. The root of Sedum plumbizincicola significantly improved the activity of Zn and Cd of the rhizosphere soil, and the addition of fertilizer enhanced the Cd activation, the enhacnce efficiency were higher than that of Zn. The conventional fertilization and the best fertilization scheme (N1P1K2) resulted from the orthogonal experiment significantly both enhanced the biomass of the plant, but the conventional fertilization treatment had lower plant Zn concentration.The treatment 'N1P1K2' had better extraction efficiency for Zn and Cd.The zinc and cadmium hyperaccumulator Sedum plumbizincicola and a low cadmium accumulating rice cultivar "Zhongxiang No.1" were adapted, two heavy metal contaminated soils were collected, and calcium magnesium phosphate (Ca-P) and rock phosphate (P-R) were applied in the Sedum plant and rice rotating pot experiment. Meanwhile, a field plot trial was also designed to study the yields of paddy rice and its Zn and Cd concentrations in shoots and grains with different dosages of calcium magnesium phosphate. The results of pot experiment showed that the Zn and Cd uptake amount by Sedum plumbizincicola were 11.5 mg pot-1 and 0.79 mg pot-1 after the addition of P-R, which was better than Ca-P addition. The Zn and Cd concentrations increased in the brown rice after growing the Sedum plant, but the addition of Ca-P significantly decreased the Zn and Cd uptake in rice and stabilized the heavy metals in the soils, which was better than the effect of P-R.The results from field plot trial showed that Ca-P could increase rice yields as a kind of P fertilizer and also could reduce the Zn and Cd contents in brown rice by enhancing the stabilization of Zn and Cd in the heavy contaminated soils.