| Antibiotic resistance genes(ARGs)are responsible for the antibiotic resistance in microorganisms,and ARGs can be transmitted between species through horizontal gene transfer(HGT)and vertical gene transfer(VGT)with the help of mobile genetic elements(MGEs)containing integrons and transposons,and thus pose a high public health risk.Aerobic composting is a process of converting unstable waste organic matter into relatively stable humus by using microbial fermentation under artificially controlled aerobic conditions.This method can shorten the treatment time and improve composting efficiency compared with anaerobic composting,and can also reduce the abundance of ARGs and mitigate the mobility and bioavailability of heavy metals by increasing complexation.In this study,aerobic composting of swine manure was carried out under artificial conditions,and the effects of biochar and woody peat on the physicochemical properties,microbial community structure,and ARGs in the composting process were investigated,and the interrelationships among environmental factors,microbial communities,and ARGs abundance in the composting process were analyzed to provide a theoretical basis for further optimization of composting conditions and processes to promote the environmentally sound disposal and resource utilization of livestock manure and reduce the environmental risks of livestock manure composting.The main contents and results are as follows:1)Physicochemical indicators such as temperature,p H,and conductivity were examined to study the effects of biochar and woody peat addition on compost products.The results showed that temperature was one of the main factors affecting the efficiency of aerobic composting,and the addition of biochar and woody peat increased the maximum temperature and duration of high temperature in the thermophilic stage of the pile compared with the control treatment.p H,C/N,and electrical conductivity varied in a similar trend during the composting process in all treatments,and all the compost products met the maturation criteria.In addition,the DTPA-extracted Cu and Zn contents in the mature compost were lower in the treatments with biochar and woody peat addition than in the control treatment,indicating that the addition of biochar and woody peat could reduce the bioavailability of heavy metals to some extent and may in turn affect the ARGs during composting.2)The effects of biochar and woody peat on microbial community structure during composting were investigated based on 16 S r RNA high-throughput sequencing technology.The results showed that the chao1 index in mature compost of each treatment group was reduced by29.4%～53.0% compared to pristine pig manure(PM),which indicated that the composting process reduced the abundance of microbial communities.There was no significant difference in shannon index among different treatments throughout the composting process,and the addition of biochar and woody peat did not affect the microbial diversity in the composting process.At the same composting stage,no significant difference was observed in microbial community structure between treatments with and without biochar and woody peat additions.The effects of physicochemical properties on microbial community structure in the biochar and woody peat treatments were consistent with those of the control treatment.Temperature and p H were important influencing factors on microbial community composition,and other environmental factors such as TN,DTPA-Cu,and DTPA-Zn were also related to microbial community structure.3)The direct and indirect effects of biochar and woody peat addition on the abundance of ARGs during composting were investigated by quantitative analysis of ARGs,MRGs,and MGEs in compost products using high-throughput fluorescence quantitative PCR.It was shown that the total relative abundances of ARGs and MGEs were reduced by 14.5%-76.4% and35.6%-89.9%,respectively,and MRGs were almost completely removed(with removal of97.6%-100%)in the mature compost of all composting treatments compared to PM,and only the resistance genes in the control treatment did not show a significant rebound trend during the composting process,indicating that to some extent the addition of biochar and woody peat could provide a suitable environment for the regeneration of host microorganisms during the composting decay stage.There was no significant difference in the composition of ARGs between the treatments with biochar and woody peat addition and the control treatment at the same stage.The effect of physicochemical properties on ARGs in the treatment with the addition of biochar and woody peat was consistent with that of the control treatment,and environmental factors such as p H,EC,and temperature could all be direct or indirect factors leading to the changes in ARGs and microorganisms.The addition of biochar and woody peat hindered the association between microorganisms and ARGs/MGEs,and thus inhibited the HGT of ARGs among different microorganisms compared to the control treatment.The addition of high level percentage(10%)of biochar and low level percentage(5%)of woody peat led to changes in ARGs,MGEs and microbial communities to some extent compared to the control treatment. |
