Development Of Microbial Fertilizer For Enhancing Phytoremediation Of Cadmium-contaminated Soil Using Accumulator Solanum Nigrum

With the development of society,human beings have increased the mining,smelting,processing and commercial manufacturing of heavy metals,and heavy metal pollution has become increasingly serious and becoming a global ecological security issue.Bioremediation is one of the economic,effective and environmentally friendly methods for remediation of heavy metal pollution.The combination of microorganisms and plants can be used to enhance the bioremediation effect by using microorganisms to promote the accumulation of heavy metals and the extraction of heavy metals.In this study,a highly efficient growth-promoting strain PGP6(Pantoea.sp)was screened from heavy metal contaminated soil in Qixiashan Manganese New Village,Nanjing,and a complex microbial agent was prepared from the high-efficiency strain A5(Bacillus.sp)screened in the laboratory.We select the optimum fermentation conditions for the complex bacteria.At the same time,the composite fungicide is mixed with the organic fertilizer grass ash in proportion to prepare the bacterial fertilizer.Pot experiments were carried out using in-situ contaminated soil to evaluate the repair effects of composite microbial agents and bacterial fertilizers.The specific results are as follows:1.Screening for strain PGP6 with Cd tolerance(0.5 mM)from in-situ contaminated soil collected in Qixia Mountain,Nanjing,PGP6 is Pantoea.sp,which can produce IAA,iron-producing carrier,ACC deaminase,and it has nitrogen-fixing properties,so the bacteria have potential growth-promoting properties.The strain was prepared by treating the Solanum nigrum L.,and the biomass of S.nigrum was increased by 1.4 times compared with the untreated group,and the cadmium accumulation was increased by 1.3 times.The high-efficiency strain A5(Bacillus.sp)screened in the previous stage of the laboratory was combined with PGP6 to prepare a composite microbial agent.The results showed that the amount of organic acid produced by the composite microbial agent was significantly increased in quantity and species compared to the single microbial agent.2.By studying the growth conditions of the strain,it was found that pH=8 is the optimum pH for PGP6 growth,and the composite microbial agent can grow well in the range of pH6-9,under the condition of 0.01%～2%salt stress.The composite microbial agent owns higher biological activity,indicating that the composite microbial agent can effectively enhance the environmental tolerance of the strain.According to the different growth conditions of the composite bacteria,the response surface analysis method was used to design the experiment,and the data reliability analysis was carried out according to the second-order regression equation.Finally,the optimal fermentation conditions of the composite microbial agent were obtained:pH=8,temperature 25℃,rotation speed 250 rpm.3.The composite fungicide was mixed with the organic fertilizer grass ash in proportion to prepare the bacterial fertilizer,and the bioremediation effect of the bacterial fertilizer and the composite microbial agent was compared.The results showed that under the bacterial fertilizer treatment,the accumulation of Cd in the shoot increased by 1.2 times compared with the composite treatment group.In addition,the plant height under the bacterial fertilizer treatment increased by about 1.22 times compared with the composite microbial treatment group;the fresh weight of the aerial part increased significantly 1.79 times compared with the composite microbial treatment group;the dry weight of the aerial part and the composite microbial treatment group The ratio increased by 1.15 times.It can be seen from the application of the bacterial fertilizer and the soil effective state of the microbial agent that the effective state of Cd in the soil under the bacterial fertilizer treatment is significantly increased by 1.10 times compared with the composite microbial treatment group,and a single microbial agent and organic fertilizer treatment can be observed.Not significantly increased.The transfer coefficient(TF)under the bacterial fertilizer treatment increased compared with the composite bacterial treatment group.The enrichment factor(BCF)of bacterial fertilizer treatment was significantly increased by 1.26 times compared with the composite microbial treatment group.