| Due to the influence of the long-term development of industrial activities,the heavy metal pollution of cultivated land soil is very serious,especially for cadmium.In recent years,biochar has received more and more attention due to its excellent properties such as high-efficiency fixation of cadmium,environmental friendliness,and improvement of soil fertility.Previous studies focused on the chemical mechanism of biochar's influence on soil heavy metal morphological transformation,but insufficient attention was paid to the mechanism of biochar's influence on microbial community of agricultural land soil with different levels of cadmium pollution.Therefore,in this study,rice straw biochar(RSB)and rice husk biochar(RHB)were added to three types of low(Soil-L),moderate(Soil-M)and heavy(Soil-H)cadmium pollution,respectively.The dynamic changes of cadmium species,soil properties,and microbial community structure were investigated via passivation culture of agricultural soil.The main findings are as follows:(1)The pH value and contents of C,H,N of rice husk and rice straw biochar prepared at the pyrolysis temperature of 700?were not significantly different,but the specific surface area of RHB(199.15 m~2/g)was 51.6 times that of RSB(3.86 m~2/g).Compared with the control(CK),RSB decreased the content of acid-extracted cadmium in Soil-L,Soil-M and Soil-H by21.3%,20.8%and 11.4%,respectively,while RHB decreased that by 24.8%,27.2%and 13.6%,respectively.Among the three soils,the dosage of 5%(w/w)of RSB and RHB were more suitable for remediation of slightly and moderately cadmium-contaminated agricultural land.In addition,biochar indirectly reduced the availability of cadmium mainly by regulating the microbial community in Soil-L and Soil-M,while biochar reduced bioavailable cadmium mainly through its own direct adsorption in Soil-H.(2)Except for ammonium nitrogen (AN) and invertase,the application of the two biochars significantly increased p H(0.4?2.78 units),soil organic matter(SOM)(0.40?1.89times),cation exchange capacity(CEC)(0.11?4.10 times),available phosphorus(AP)(0.19?1.72 times),available potassium(AK)(0.37?9.61 times)and catalase content(0.06?2.85 times)in the three soils.Their promoting effect on soil organic matter was similar,and rice straw biochar displayed superiority over rice husk biochar in enhancing the remaining soil properties.The changes of the soil properties may affect the transformation of cadmium speciation in soil.(3)The application of RSB suppressed the richness and diversity of bacterial communities in the three soils,and decreased the association between the microbial communities in Soil-L and Soil-M.p H,SOM and CEC were the key factors affecting bacterial community structure in Soil-L,while SOM,CEC,p H and BF-Cd were the dominant factors affecting bacterial community composition in Soil-M and Soil-H.Enzyme activity played an important role in influencing the structure of soil fungal communities.The application of RHB inhibited the bacterial community richness in Soil-L,but increased the bacterial community richness and diversity in Soil-M along with that of fungal community in the three soils.The association between microbial communities was also enhanced in Soil-L and Soil-H after applying RHB.Besides,BF-Cd and sucrase were the key factors affecting the bacterial community in Soil-L;BF-Cd and p H were the key factors affecting the bacterial community in Soil-M;SOM and sucrase were the key factors affecting the bacterial community in Soil-H after applying RHB.However,catalase was the only environmental factor that significantly affected the composition of fungal communities in Soil-L and Soil-M. |
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