Enhancing Phytoremediation Of Cadmium Contaminated Soil By Bacillus Megaterium And Organic Materials

Cadmium（Cd）pollution of farmland soil is a threat to agricultural safety and human health,had a widespread concern among people.Phytoextraction of Cd-contaminated soils with hyperaccumulator Sedum plumbizincicola is considered to be an environmental friendly remediation technology,compared with the physical and chemical remediation technologies.However,the phytoextraction efficiency of Sedum plumbizincicola is always limited because of the slow growth and low Cd availability of soils.Taking some strengthening measures can effectively improve the phytoextraction efficiency and shorten the remediation period.In this study,Cd-contaminated acid farmland soil in Hunan Province was used as the remediation object.A Bacillus megaterium strain screened from the roots of Sedum plumbizincicola was used as the material to study its effect on the remediation efficiency of Sedum plumbizincicola.The mechanism of enhancing the remediation of Sedum plumbizincicola was preliminarily discussed,and the high efficiency enhanced remediation technology mode was screened combined with organic materials.The main results as following:（1）Inoculation of Bacillus megaterium can effectively improve the phytoextraction efficiency of Sedum plumbizincicola on Cd-contaminated acid farmland soils.A strain of Bacillus megaterium isolated from the root of Sedum plumbizincicola,was used to analyze the effect of different inoculation amount of Bacillus megaterium on the remediation efficiency of Cd-contaminated farmland soil by Sedum plumbizincicola.The results show:Inoculation of Bacillus megaterium promoted the growth of Sedum plumbizincicola,and the biomass of shoots and roots increased by8.7%～66.7%and 13.6%～81.8%respectively compared with the control;Bacillus megaterium improved the soil Cd availability,promoted the absorption and accumulation of Cd in Sedum plumbizincicola,and shoot Cd concentration increased by 29.2%～60.4%.Under the conditions of Sedum plumbizincicola inoculated with Bacillus megaterium,Cd removal rate of soil reached 26.7%～42.9%,and M₄treatment has the best remediation effect,which indicates that the phytoextraction efficiency of Sedum plumbizincicola is also affected by the amount of bacteria.（2）The effect of organic materials on the remediation of Sedum plumbizincicola is closely related to its type and application rate.A pot experiment was conducted to investigate the effects of four organic materials（rice straw,soybean straw,pig manure,and dissolved organic fertilizer.）,and their application of 1%and 3%of soil on the phytoremediation efficiency of Sedum plumbizincicola.The application of organic materials promoted the growth of Sedum plumbizincicola:shoot and root biomass increased by 1.08%～40.69%and 4.17%～54.17,respectively,compared with the control.The treatments of adding rice straw,soybean straw and dissolved organic fertilizer improved Cd concentration in Sedum plumbizincicola shoots and roots by10.02%～64.91%and 10.95%～45.78%,respectively.Among all the treatments,3%rice straw and dissolved organic fertilizer had the most significant effect on the phytoextraction of Cd-contaminated farmland soil by Sedum plumbizincicola,and the Cd removal rate were 49.3%and50.7%respectively.（3）Through the experiment of Bacillus megaterium combined with organic materials,it was found that the combination of Bacillus megaterium and rice straw had the best effect on the phytoextraction of Cd-contaminated soil by Sedum plumbizincicola.Compared with the control,shoots and roots biomass increased by 106.4%and 240.0%respectively,and Cd concentration increased by 71.96%and 27.99%respectively.Soil Cd removal rate reached 47.11%.This study revealed the mechanism of enhanced remediation of Sedum plumbizincicola by Bacillus megaterium and organic materials.The selected Bacillus megaterium-rice straw combined enhanced remediation model has certain guiding significance for the efficient remediation of Cd-contaminated farmland soils by Sedum plumbizincicola.