| Livestock and poultry manure was applied to soil as organic fertilizer for a long time,and the residual heavy metals and antibiotics seriously threaten soil health.Therefore,pollution caused by heavy metals and antibiotics has attracted more attention and has become a new hot spot in environmental science.To explore the remediation effect of biochar on contaminated soil,apple branches,corn straw and millet straw were used as raw materials in this study to prepare biochar at different pyrolysis temperatures(300,450 and 600°C).The biochar with the best adsorption effect at pyrolysis temperature was screened from this three raw material biochar,modified with H3PO4 and used for adsorption and pot experiments.The pot experiment was conducted by simulate contaminated soil with exogenous addition of Cd(NO3)2·4H2O and OTC·HCl,in which Brassica chinensis L.was used as test material.This study investigated the effects of different biochar(screened apple branches,corn straw and grain straw with optimal pyrolysis temperature raw biochar and H3PO4 modified biochar)on the physiological characteristics of Brassica chinensis L.and physicochemical properties of soil.The residue characteristics of OTC,Cd and tetracycline resistance genes in the soil-plant system were also investigated.This study can provide a scientific basis for applying biochar in the remediation of OTC-Cd composite contaminated soil,give a reference for the safe production of vegetables,and provide an effective way for the resource utilization of agricultural waste.The main research results were as follows.(1)The best adsorption effect of apple branches,corn straw and millet straw biochar prepared under 600°C pyrolysis conditions on OTC and Cd,and the maximum adsorption of OTC was achieved by H3PO4 modified millet straw biochar at 600°C;(2)OTC-Cd contamination affected the antioxidant enzyme activity of Brassica chinensis L.and reduced the quality of Brassica chinensis L.,while there was no significant effect on the nutrients of Brassica chinensis L.The addition of biochar could alleviate the toxic effect of OTC-Cd compound pollution on Brassica chinensis L.and improve the quality of Brassica chinensis L.;(3)OTC-Cd significantly inhibited soil catalase,urease,sucrase,alkaline phosphatase and dehydrogenase activities and reduced soil p H and cation exchange capacity,while there was no significant effect on other soil fertility indicators.The addition of biochar could alleviate the inhibitory effect of OTC-Cd on soil enzyme activities,and the activation of soil enzyme activities by apple branch biochar and millet straw biochar was better than that by corn straw biochar,with the most significant increase of 41.19% on soil dehydrogenase;(4)In all added biochar treatments,OTC and Cd were reduced in both root and shoot of Brassica chinensis L.,and the residual in different tissues varied greatly,root >shoot.Biochar can reduce the residues of OTC and Cd of Brassica chinensis L.,and reduce the content of OTC and DPTA Cd in soil,and change the exchangeable Cd to organic and residual Cd.The relative abundance of antibiotic resistance genes in the soil-plant system varied greatly,and the residual patterns of different genes in different tissues of Brassica chinensis L.were different.tet M was the most abundant gene in soil and plant,followed by gene tet B.Biochar increased the relative abundance of Proteobacteria、Planctomycetes、Gemmatimonadetes and Firmicutes at the phylum level,and increased the relative abundance of RB41,Cellvibrio,and Altererythrobacter at the genus level increased by 261.39%,161.80%,121.43%,and 63.33%,respectively;(5)The remediation effect of millet straw biochar on polluted soil and water solution was better than apple tree branches and corn straw biochar. |
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