[Uptake and distribution of Cu, Zn, Pb and Cd in maize related to metals speciation change in rhizosphere].

The behavior of heavy metals in terrestrial system and the mechanism of VAM plant in toleranting excessive heavy metals in soil were examined with VAM maize(Zea mays L.). After seven-week cultivation in sewage-sludging soil, the biomass of VAM (Glomus mosseae) maize was found 1.5 times higher than non-mycorrhizal one. Compared with non-mycorrhizal maize, the accumulation of Cu, Zn and Pb by mycorrhizal maize was reduced by 10%, 18% and 29%, respectively, but the accumulation of Cd was the same. The distribution and speciation change of Cu, Zn, Pb and Cd in rhizosphere of VAM and non-mycorrhizal maize were analyzed by using the technique of sequential extraction. Except a significant increase in exchangeable Cu in rhizosphere of VAM maize, the increased amount of test metals bound to organic matter, carbonates, iron and manganese oxides were significantly higher than those in rhizosphere of non-mycorrhizal maize, indicating that the speciation of metals in rhizosphere of mycorrhizal maize growing in contaminated soil tended to be relatively stable. Meanwhile, the influence of metal speciation in rhizosphere on its bioavailability as well as the mechanism of mycorrhizal plant in toleranting excess metals were also discussed.