Effects Of Polluted Soils Amendments On The Uptake Of Cd,Zn,Pb And Cu By Eucalyptus

The research samples were six mine/farmland soils surrounding mine area in Hechi city of Guangxi province and the eucalyptus. Used the soil samples and the eucalyptus to do the pot experiment, in order to know how the bagasse biochar and red mud in different ratios acts on eucalyptus absorb the cadmium (Cd), zinc (Zn), lead (Pb) and copper (Cu). By the wet digestion method and BCR sequential extraction procedure, we could obtain the contents and speciation distribution of heavy metals (Cd, Zn, Pb and Cu) and the status of pollution in the soil samples. This research studied the eucalyptus response and tolerance mechanisms to the heavy metal stress by used thiobarbituric and a mixed solvent of acetone and ethanol to extract malondialdehyde (MDA) and chlorophyll. In this article also discussed the soil amendments changes to heavy metal contents in the eucalyptus. Eucalyptuses were cultivated in the soil samples which added different amounts of modifier and harvested after 12 weeks. The biomass, chlorophyll content, MDA and heavy metal content in different parts of eucalyptus were determined respectively. The main results are as follows:(1) The heavy metals in samples had some enrichment effect. The contents of heavy metals were higher than the background values in the local area and the soil environmental quality standard (SEQS). The pollution level showed the sequence Cd>Zn> Pb= Cu according to the multiples (total heavy metal in soil:SEQS).The results of BCR method showed the extractable heavy metals in five sampling points near the mines were account for 50% of the total amount at least, so the extractable heavy metals had strong bioavailability and toxicity. The heavy metals in the farthest sampling point were mainly found in residual form (> 60%), the heavy metals in extractable form were less than 40%.(2) Adding soil conditioner could change the chemical speciation of heavy metals in the soil, so that making Cd, Zn, Pb and Cu transform active form to stable form and reducing Cd, Zn, Pb and Cu activity and bioavailability. Comprehensive experimental results, the modifier G3 is better for eucalyptus tolerance Cd, Zn, Pb or Cu. And the effect of reduce Cd, Zn, Pb and Cu activity is better than G1 and G2.(3) Adding modifier could reduce the effect of heavy metal stress on the growth of eucalyptus, increasing biomass and chlorophyll content of eucalyptus. Adding 5% modifier of G3 (bagasse biochar and red mud ratio of 2: 1) enabled the eucalyptus underground biomass increased up to 159%; adding 2% modifier of G3 enabled eucalyptus aboveground biomass increased up to 154%. Adding 2% modifier of G3 could significantly increase chlorophyll content compared to other groups, to increase 8% to 23%.(4) MDA is the product of a plant under stress conditions of membrane lipid peroxidation. The contents of MDA in eucalyptus are proportional to concentrations of heavy metals in soil, and significantly affected by the heavy metals of weak acid extraction condition. Applying a modifier enabled contents of MDA significantly decreased. Adding 1% modifier of G3 effect more pronounced.(5) 67.7%～94.8% of Cd or Pb were accumulated in underground part of eucalyptus; transfer to the aboveground part was less. The Zn and Cu in the eucalyptus were more evenly distributed in underground and aboveground parts. Adding the conditioner on soil had a little influence on absorption of zinc, bigger influence on the Cd, Pb and Cu.