Effects of arbuscular mycorrhizal fungi on heavy metal tolerance of clover in contaminated soil EFFECTS OF COMPOUND POLLUTION OF ZINC AND CHROMIUM ON SOIL ENZYME ACTIVITY AT DIFFERENT GROWTH STAGES OF RICE PLANT Ecological effect of exotic Cd-Zn compound pollution on purple soil Effect of single eleLent and coLpound pollution of Cd,Zn,Pb on soil catalase activity Ecological effect of compound pollution of heavy metals in soil plant system Ⅱ. Effect on element uptake by crops, alfalfa and tree Ecological effect of compound pollution of heavy metals in soil-plant system Ⅰ.Effect on crop, soil microorganism, alfalfa and tree Effect of Cu and Zn Compound Pollution on Antioxidant Enzyme Activity of Cu-enrichment Plant Myriophyllum aquaticum