| As an emerging environmental pollutant,the proliferation and diffusion of antibiotic resistance genes（ARGs）in the environment has attracted extensive attention of scholars at home and abroad.The long-term abuse of antibiotics in livestock and poultry breeding industry has led to livestock and poultry manure becoming an important repository of ARGs,and the continuous application of manure in agricultural production has increased the input of ARGs to soil.Soil-plant system is an important way for ARGs to spread from the environment to humans,and raw edible vegetables have become one of the sources of humans exposed to environmental ARGs.Therefore,it is of great significance to study the effect of manure application on the migration of ARGs in the soil-plant system and explore the prevention and control methods of ARGs in the soil-vegetable system,so as to reduce the antibiotic resistance pollution of soil ecological environment and the exposure risk of ARGs in vegetables to humans.In this study,through pot experiment,different chicken manure application ratios（1%,3% and 8%）and 2% rice husk biochar addition treatment were set to explore the effects of chicken manure application on the abundance of ARGs in the soillettuce system,analyze the changes of community structure of soil bacteria and bacteria in lettuce tissue,and screen the key factors affecting the distribution of ARGs in soil and lettuce tissue by using real-time quantitative PCR（q PCR）and Illumina high-throughput sequencing technology.Furthermore,the migration of ARGs in the soil-lettuce system was regulated by the addition of biochar,so as to explore the internal mechanism of biochar preventing and controlling the spread of ARGs.The main conclusions are as follows:（1）Chicken manure application increased the total relative abundance of ARGs and mobile genetic elements（MGEs）in the soil-lettuce system,and biochar effectively reduced the migration of ARGs in soil.The application of chicken manure increased the total relative abundance of ARGs and MGEs in non-rhizosphere soil,rhizosphere soil,lettuce roots and leaves.Among them,the enrichment multiples of ARGs and MGEs in rhizosphere soil were up to 883.4 times and 29.6 times,respectively.Biochar reduced the accumulation of ARGs and MGEs in the soil-lettuce system.Among them,the total relative abundance of ARGs in non-rhizosphere soil,rhizosphere soil,lettuce roots and leaves decreased by 76.43%,99.39%,27.31%and 25.84%,respectively,and the total relative abundance of MGEs decreased by28.30%,74.88%,36.82%and 27.91%,respectively,indicating that biochar addition may be an effective way to alleviate the diffusion of ARGs in soil and migration to plants.（2）The similarity of microbial community composition between chicken manure and soil-lettuce system indicates that ARGs may diffuse in the soil-lettuce system with microorganism as medium,and biochar can regulate the migration of ARGs by changing the microbial community structure of the soil-plant system.The addition of chicken manure and biochar changed the bacterial community composition of soil and lettuce tissue to some extent.Proteobacteria,Firmicutes and Actinobacteria are the dominant bacteria phyla in soil,while Proteobacteria is also the dominant phyla in lettuce tissue,accounting for 93.13%-96.64% and 79.40%-87.43% of the total bacterial abundance in lettuce roots and leaves,respectively.Chicken manure application decreased the abundance of Proteobacteria and Actinomycetes and increased the abundance of Firmicutes in soil,while biochar addition increased the relative abundance of Proteobacteria in lettuce roots and decreased the relative abundance in leaves.Therefore,manure or biochar addition may affect the occurrence of ARGs in the soil-plant system by affecting the composition of microbial community.（3）Soil p H,organic matter,total nitrogen and total phosphorus content and the accumulation of heavy metals Cu and Zn in soil caused by manure application could affect the distribution of ARGs in soil.Various types of ARGs in soil and lettuce tissue were significantly positively correlated with integrase genes int I1 and int I2,indicating that chicken manure may lead to the diffusion of ARGs by promoting horizontal gene transfer（HGT）,and the effect of MGEs on the horizontal transfer of ARGs in soil was more significant than lettuce tissue.In addition,a large number of potential host bacteria of ARGs and MGEs were detected in non-rhizosphere soil,rhizosphere soil,lettuce roots and leaves,indicating that the evolution of bacterial community structure may be an essential mechanism driving the migration of ARGs in manure-improved soil-plant system,which provides a theoretical basis for evaluating the transmission of ARGs in soil and plants in agricultural production. |
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