Effects Of Biochar Application On Variation Of Antibiotic And Antibiotic Resistance Genes In Soil

In recent years,the abuse of antibiotics in the livestock breeding induced the occurrence of Antibiotic Resistance Genes(ARGs),which led to the soil acception to faeces being the repository of antibiotic and ARGs.Antibiotics and ARGs could be threat to human health through food chain.Biochar was commonly used as a conditioner and pollution repairing additive for cropland soil,but it was unclear that the effects of biochar on the accumulation and transport of the antibiotics and ARGs in soil and plant.Therefore,the study investigated occurrence of antibiotics and ARGs in soil for three kinds of livestock and poultry farms(pig,chicken and beef cattle),and analyzed the main factors affecting the ARGs distribution.In addition,using oxytetracycline(OTC)as a typical pollutant,isothermal batch adsorption experiments were established to study the effects of different kinds of biochar on soil adsorption OTC.Soil cultivating experiments were conducted to elucidate the degradation and variation of OTC and ARGs in soil applied biochar with the strongest adsorption property.The pot experiment further analyzed the transport and accumulation of OTC,ARGs and intI1in the biochar soil applied biochar and lettuce,and revealed the mechanism of microbiology affecting the distribution of ARGs.The results of this study provided theoretical basis for evaluating the ecological risk and reducing their harmful of antibiotics and ARGs in soil.The main research conclusions were as follows:(1)The soil for manure stacking and farmland utilization at livestock and poultry farms contained a large amounts of ARGs,antibiotics and heavy metals.The contents of ARGs,antibiotics and heavy metals were the highest in soil for pig manure dumps,followd by the chicken farms,and least in beef cattle farms.The absolute abundance of ARGs in the soil for livestock and poultry farms were more than 2.62 times than that of the farmland soil without manure.In 11 kinds of ARGs,the absolute and relative abundance of enzyme modifier gene(tetX)were the highest,followed by the ribosomal protection gene(sul1 and sul2)and the external pump gene tetG,which were the dominant genes in soil of livestock and poultry farms.The concentration of tetracycline antibiotics in soil of manure dumps was 0.15~4.76mg/kg,and the concentration of sulfonamides was 0~2.62 mg/kg,which were significantly greater than that of the farmland soil without manure.Structure analysis of soil bacteria showed that bacterial genus level of soil for manure stacking and farmland utilization was very different from farmland soil without manure,mainly in the difference form Actinomadura,Lysobacter,Flavobacterium,Bacillus,and so on.Redundancy analysis and Network analysis showed that soil copper and zinc,Actinobacteria and total tetracycline antibiotics were the main reasons for the difference ARGs distribution differences in soil of livestock and poultry farms.(2)Three typical agricultural wastes(wheat straw,corn straw and apple tree branch)were used as starting material to make the biochar under 500℃,and the physical and chemical properties of the three types of biochar were measured.The results showed that the cation exchange capacity(CEC)of the apple tree branch biochar was higher than the wheat straw and corn straw biochar.The carbon content of apple tree branch biochar(66.1%)was1.9 and 1.3 times higher than the wheat straw and corn straw biochar.Three types of biochar had flourishing hole structure and the superficial area of apple tree branch biochar(126.6 m~2/g)was 1.7 and 48.7 times higher than the wheat straw and corn straw biochar.In brief,compared with the other two types of biochar,apple tree branch biochar had the higher aromatization structure and specific surface area.Thus the apple tree branch biochar was more suitable to be used to soil remediation.(3)Three types of biochar improved the adsorption capacity of soil to OTC.The largest adsorption capacity to OTC was achieved by the apple tree branch biochar,reaching to 4.24mg/g.The Freundlich model well matched the process that biochar adsorbed OTC(R~2>0.9).The adsorption of OTC by soil added biochar was dominated by distribution,followed by surface adsorption ofπ-πelectron donor-receptor action.The quasi-second-order kinetic model could well match the adsorption kinetics process of OTC in the biochar addition soil(R~2=1).The absorption process could be divided into the early rapid reaction stage and the middle and later slow-speed balance stage.The pH,ion strength and copper concentration in soil solution affected the OTC adsorption by the biochar added to soil.(4)Biochar made from apple tree branch increased the degradation rate of OTC,shortened the half-life of OTC for 60 days.The absolute and relative abundance of tetG in soil was the highest,which was the dominant gene of tetracycline resistant genes.Biochar reduced the relative abundance of tetG and total tetracycline resistance genes.AWCD was decreased gradually with the increase of soil incubation time.At the 60 d,the activity of microbial carbon metabolism of soil applied biochar was greater than that treatments without biochar.Pearson correlation showed that the decrease of ARGs abundance in soil was significantly correlated with carbon metabolism of bacterial community and degradation of OTC(P<0.05).(5)Biochar was an effective soil amendment,which decreased the accumulation and transport of OTC in the soil as well as lettuce roots and leaves,and it also reduced the abundances of ARGs and Human pathogen bacteria.Biochar applied to contaminated soil at an OTC concentration of 300 mg/kg significantly reduced the OTC content by 10.66%、39.0%and 30.1%(P<0.05);the relative abundances of ARGs were decreased by 44.1%,51.8%and43.4%in lettuce leaves,roots,and soil,respectively,compared with not adding biochar soil.The application of biochar had no significant effects on intI1.Bacterial community succession was the main mechanism that affected the variation in ARGs and intI1.The reduction of Firmicutes in the soil and lettuces under the biochar treatment might lead to decreases in tetracycline resistance genes in the leaves.In conclusion,the soil for manure stacking and farmland utilization at livestock and poultry farms contained a large amounts of ARGs,antibiotics and heavy metals.Biochar made by apple trees branch increased the soil adsorption on OTC,accelerated OTC degradation by biological and non-biological mechanism in soil,and reduced the accumulation and transport of OTC and ARGs in soil as well as lettuce roots and leaves.Therefore,biochar was an effective soil amendment,which could alleviate the human health threat of OTC and ARGs in the environment.