| The possible use of energy plant for bioremediation of heavy metal contaminated soils was suggested considering the limitation of current practicable soil remediation strategies and the complexity of heavy metal contaminations. Systematic studies on the critical role of plant growth promoting bacteria (PGPB) in metal translocation from soil to plants, with focuses on the mechanisms of metal phytotoxic alleviation by PGPB, were conducted on a contaminated calcareous soil.Hydroponic experiments were used to study the effects of different concentrations of Cd treatment on two hemp cultivars. Result showed that:Hemp grown better under low concentration (Cd<20μmol/L), but it would be poisoned when the concentration of heavy metals over the critical concentrations. Plant height, root length, fresh and dry biomass and injured roots all decreased markedly with increasing Cd concentrations (p<0.05). The chlorophyll content and water content in hemp leaves also reduced gradually with increasing Cd concentrations. The tolerance index (TI) of two hemp cultivars on different growth parameters is over50. We got the semilethal concentration of Cd for the two hemp cultivars from the fitting curves of their growth parameters, Luan hemp was grown better than USO-31.Simulation of Cd contaminated soil pot experiment:JP3-3of endophytic bacteria and rhizosphere bacteria J62can promote the growth of two hemp cultivars. Total root volume, total root surface area, total root length, root tips and forks number were all significantly increased (p<0.05). The use of PGPB increased the total chloroPhyll content、root activity of hemp; and reduced the proline content, the MDA content. Cd accumulation capacity of USO root was significantly lower than Luan hemps’, the TI was no differencnce. This study showed that:the JP3-3had better promoting effect on shoot, J62had more effective activation of heavy metals in the soil, increased the bioavailability of Cd in soil and promotion Cd absorption and accumulation in the hemps. On Zn, Cu and Cd contamination soil, the use of PGPB (JP3-3and J62) could alleviate membrane lipid peroxidation, enhance roots vitality, increase the total root surface areas and root number, which stimulated the growth and alleviated hemp suffer heavy metal poisoning. Inoculation process can increase heavy metal accumulation in hemp plants, PGPB and hemp root exudates could reduce the soil pH and dissolve heavy metals to improve the bioavailability, especially in J62treatments (p<0.05).In summary, the use of PGPB enhanced the heavy metals resistance of hemp, and increased the content of heavy metals under the single stress (Cd) or complex heavy metals (Zn, Cu and Cd) contaminated soil. This research has an important theoretical and practical significance for the application of complex heavy metal pollution. |
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