| The intensive development of breeding industry has produced a lot of livestock wastewater.The livestock wastewater could be used as organic fertilizer to improve soil,which meets the resource recovery of livestock manure.However,the antibiotic resistance genes(ARGs)in livestock wastewater could also enter the soil,increasing the ecological risk of ARGs in soil.To study the effects of manure application on occurrence of ARGs in soil,two-year field experiments were carried out with different fertilization schemes.14 subtypes of ARGs had been detected to investigate the effects of environmental factors,mobile gene elements(MGEs)and microbial communities on the occurrence of ARGs in manure-applied soil and to explore the main driving factors.Then the risks of ARGs in manure-applied soil were assessed.The main results are as follows:(1)14 subtypes of ARGs were detected in livestock wastewater.After manure application,the types of ARGs in the soil were consistent with those in the background soil,including tetC,ermB,ermF,sul2 and dfrA1.The amount of livestock wastewater which returned to the soil had little influence on the ARGs,whereas the absolute abundance of ARGs in soil increased by 4.70%～47.64% than that in the background soil,which was consisted with the increase of abundance of ermF.Double factor variance analysis showed that the fertilization years had a greater effect on ARGs changes in the manure-applied soil than the fertilization rates.Correlation analysis showed that the organic matter,total nitrogen,total phosphorus,intI1 and intI2 had significant positive correlations with ARGs.(2)There were significant differences in bacteria and fungi community composition and diversity in manure-applied soil over 2 years,but different amount of livestock wastewater had little effect on soil microbial community structure.After livestock wastewater application in the first year,bacteria such as unspecified＿Gemm＿5 and Steroidobacter became the dominant groups in soil under different fertilization schemes.In the second year,Skermanella,Bacillus and Arthrobacter in the soil become the dominant bacteria.Network analysis showed that the number of host microorganisms of ARGs decreased from 34 types to 11 types in two years.However,the relative abundance of host bacteria increased significantly,especially the abundance of Skermanella and unspecified＿JG30＿KF＿CM45 who were the potential hosts of ermF,increased by 6.45%～17.85% and 1.60%～5.29%,respectively.That two genes affected the abundance of total ARGs in the soil.Redundancy analysis and partial least square were used to study the effects of 15 important factors on the abundance of ARGs.The results showed that the change of soil bacteria had the greatest influence on the occurrence characteristics of soil ARGs.(3)The pollution index was used to evaluate the ecological risk of ARGs in soil.The pollution index of ermF and ermB in soil increased significantly after livestock wastewater application after two years,which were the two types of genes with high risk.The comprehensive pollution index of ARGs increased significantly under different amounts of livestock wastewater,indicating a cumulative risk of ARGs in soil.There was a significant positive correlation between intI1 and intI2 and ARGs in soil in the first year and the second year,respectively.There was a horizontal transfer risk of ARGs in soil with livestock wastewater application.The potential risk of ARGs in soil was further discussed and the control measures were put forward,so as to provide a scientific basis for the safe reuse of farmland soil. |
