Effects Of Biochar Combined With Cd-tolerant Bacteria On Remediation Of Cd-contaminated Soil And Safe Production Of Cabbage

Cd pollution in farmland soil not only seriously hinders the safe production of agricultural products in China,but also poses a great threat to the health of the ecosystem.Single remediation technology has its limitations.In order to realize the safe utilization of moderate and mild Cd contaminated farmland soil,multiple materials composite remediation can be used to ensure the quality and safety of agricultural products.In this study,a strain M6 with better adsorption of Cd²⁺was isolated from heavily Cd contaminated soil.The mechanism of Cd²⁺removal in liquid medium was discussed by SEM-EDS,FTIR,XPS analysis and the distribution of intracellular and extracellular Cd in M6.The soil culture experiment showed that the inoculation of strain M6 could effectively reduce the content of DTPA-Cd in soil.Therefore,in this paper,using corn straw biochar,pine biochar and M6 bacterial inoculum as experimental materials,a pot experiment was conducted to study the effects of single and compound treatments of1%and 2%corn straw biochar and pine biochar,M6 microbial inoculum on the basic physicochemical properties of moderately and mildly Cd contaminated soil,enzyme activity,DTPA-Cd content,growth,yield,quality and Cd accumulation of cabbage.Furthermore,the remediation effect of biochar combined with strain M6 on Cd contaminated soil was discussed in order to provide theoretical basis for the application of biochar with Cd tolerant bacteria in the remediation of moderately and mildly Cd contaminated soil.The main results are as follows:(1)14 strains were isolated from contaminated soil,which with stronger tolerance to Cd.By testing their adsorption effect on liquid medium Cd,one strain M6 with the best adsorption effect on Cd in liquid medium was selected and identified as Delftia sp.The optimum culture condition of M6 was 35?,p H=7,120 r/min and the mass fraction of Na Cl was 0%?1%.When the temperature is 35?,p H=7,culture time is 48 h and Cd²⁺is10 mg/L,the adsorption rate of Cd²⁺is the highest,which is 71.5%.The extracellular functional groups of strain M6 are involved in the process of Cd adsorption.The mechanisms of Cd removal in liquid medium include intracellular accumulation and extracellular adsorption.Cd²⁺exists as Cd(OH)₂on the cell surface.(2)The treatment of 2%biochar combined with bacterial inoculum had better effect on physical and chemical properties improvement of soil polluted by moderate and mild Cd.Among of them treatment of 2%corn straw biochar combined with bacterial inoculum(M-E)was the best.Soil p H significantly increas than CK(P<0.05).The CEC and available nutrients content of soil also increased clearly.The content of soil organic matter increased the most,which was 94.28%higher compared with CK.Soil DTPA-Cd content was the lowest,which was decrease 25.03%compared with CK,and significantly lower than that of 2%corn straw biochar treatment(M-D)and bacterial inoculum(A)(P<0.05).(3)The soil urease activity and sucrase activity of 2%corn straw biochar combined with bacterial inoculum treatment were the highest,68.35%and 89.93%higher than that of CK,respectively,and also significantly higher than that of 2%corn straw biochar treatment(M-D)and bacterial inoculum(A)(P<0.05).Soil catalase activity of 1%pine biochar combined with bacterial inoculum treatment(P-C)was higher than that of 1%corn straw biochar combined with bacterial inoculum(M-C).(4)The yield,root length,root weight,plant height and leaf area of cabbage were the best when treated with 2%corn straw biochar combined with bacterial inoculum(M-E).The content of soluble protein and soluble sugar in cabbage was the highest,which was significantly higher than that of 2%corn straw biochar treatment(M-D)and bacterial inoculum treatment(A)(P<0.05).The bacterial inoculum treatment(A)could increase the content of chlorophyll,which was 3.91%higher than that of CK,but the vitamin C content of cabbage in all treatments was lower than that of CK.(5)All treatments could significantly reduce the Cd content of cabbage,and the Cd content was the lowest in 2%corn straw biochar combined with bacterial treatment(M-E),which was significantly lower than the treatment of 2%corn straw biochar(M-D)and bacterial inoculum treatment(A).The Cd content of cabbage was 0.165 mg/kg,which reached the 0.2 mg/kg limit of Cd content in middle leafy vegetables stipulated in the National Standard for Food Safety(GB2762-2017).Correlation analysis showed that the Cd content of cabbage was negatively correlated with soil p H,organic matter content,urease and sucrase activity,but positively correlated with soil DTPA-Cd content.To sum up,the compound treatment of 2%corn straw biochar and bacterial inoculum has the best effect on soil improvement and remediation of moderate and mildly Cd contaminated soil,which is beneficial to improve the quality of cabbage and realizing safe production.