Phytoremediation Of Co-cropping Different Plants On Mine Soil Contaminated By Lead And Zinc

The study chosen Rumex nepalensis, Pb and Zn-hyperaccumulating plant screened in our previous experiments, ryegrass which were accumlator of lead and zinc, and common plants Trifolium repens, grown in artificial climate box with soil which contaminated by lead and zinc tailing. According to the completely randomized experiment, each treaments were repeated4times, and the controls were mono-cropping and the contaminated soil without plant. Analysised the growth conditions, physiological changes and accumulation characteristics of lead and zinc by co-cropping, discussed the restoration potential of heavy metal polluted soil by lead and zinc tailing, compared the restorative effects of contaminated soil by co-cropping, conducted to screened out the best plant collocation. The main findings are as follows:1. Three plants showed different responses by co-cropping. In compared with mono-crop, co-cropping inhibited the growth of Rumex nepalensis to a certain extent(the biomass maximum reduction rates were different, the overground part was38%, the roots were24%), Trifolium repens had the same law (the overground part was17%, the roots were25%). Co-cropping promoted the growth of ryegrass,under the collocation of Rumex nepalensis,ryegrass and Trifolium repens had the maximum biomass(overground part increased59%,roots increased62%).2. In compared with mono-crop, co-cropping increased the stress to shoots and roots of3plants, and the physiological indicators had a significant difference between different plants. Rumex nepalensis and ryegrass conquered the stress by increasing or decreasing antioxidase activities,MDA content,soluble sugars, and soluble protein content of shoots and roots while co-cropping caused physiological metabolic disorder of Trifolium repens in a certain degree.3.Co-cropping stimulated the plant absorbed nutrients than mono-crop. Co-cropping increased N and K of Rumex nepalensis, N,P, and K of ryegrass, and N of Trifolium repens. The major factor in increasing biomass was increasing of P content of ryegrass.4. Co-cropping increased the content of lead and zinc in shoots and roots, the maximum content of Rumex nepalensis were330.419mg/kg,1224.768mg/kg,1482.519mg/kg, and1998.602mg/kg; The maximum content of ryegrass were203.346mg/kg,1574.117mg/kg,922.832mg/kg, and1170.406mg/kg; The maximum content of Trifolium repens were273.973mg/kg,1070.489mg/kg,933.011mg/kg, and2350.475mg/kg. Co-cropping not increased heavy metal uptaken by Rumex nepalensis and ryegrass,but co-cropping with enrichment plants significantly increased the heavy metal in common plants-Trifolium repens, and reached the critical value of accumulation plant. Co-cropping also increased heavy metal concentration coefficient, which greater than1.5. In compared with contaminated soil without plant, in general,co-cropping increased the content of alkaline solution nitrogen, available phosphorus and available potassium in rhizosphere soil and non-rhizosphere soil, and available nutrients of non-rhizosphere soil were higher than rhizosphere soil in slightly, and the pH of soil had decreased (about1%to4%of the soil without plant), but there are no significant differences among the treatments.6. In compared with the contaminated soil without plant, planting plants could reduced the available heavy metal content, and the content in rhizosphere soils was lower than non-rhizosphere soil. Co-cropping can activate lead and zinc in soil better, and the biomass under the collocation of3plants were highest, reached7819.311mg/basin and12576.054mg/basin, the second was collocation of Rumex nepalensis and ryegrass, reached6905.358mg/basin and12526.610mg/basin.The results of this study: the best collocation was Rumex nepalensis, ryegrass and Trifolium repens for repairing contaminated soil by lead and zinc mine. The co-cropping enhanced the repair capacity of3plants as a whole repaired contaminated soil and increased biodiversity at the same time. These theories provided a theory reference for exploring the intensive measures’ application and promotion in phytoremediation of heavy metal polluting in mine soil.