Abstracts |
To understand the roles of mycorrhiza in metal speciation in the rhizosphere and the impact on increasing host plant tolerance against excessive heavy metals in soil, maize (Zea mays) inoculated with arbuscular mycorrhizal fungus (AM, Glomus mosseae) was cultivated in heavy metal contaminated soil taken from a vegetable land in Tianjin, China. Speciations of copper (Cu), zinc (Zn) and lead (Pb) in the soil were analysed with sequential extraction. The results showed that, compared with bulked soil, the exchangeable copper increased from 26 to 43% in non-infected and AM-infected rhizoshpere respectively; while the speciation of other forms (organic, carbonate and Fe-Mn oxide copper) remained constant, and the organic bound Zn and Pb also increased but the exchangeable Zn and Pb were undetectable. The organic bound Cu, Zn and Pb were higher by 15, 40 and 20%, respectively, in the rhizosphere of AM-infected maize compared with the non-infected maize. The results might indicate that mycorrhiza could protect its host plants from the phytotoxicity of excessive Cu, Zn and Pb by changing the speciation from the bioavailable to the non-bio-available form. The fact that Cu and Zn accumulation in the roots and shoots of mycorrhiza-infected plants were significantly lower than those in the non-infected plants might also suggest that mycorrhiza efficiently restricted excessive Cu and Zn absorptions into the host plants. Compared to the non-infected seedlings, the Pb content of infected seedlings was 60% higher in shoots. This might illustrate that mycorrhiza have a different mechanism for protecting its host from excessive Pb phytotoxicity by chelating Pb in the shoots. |