| dc.description.abstract | In recent years, the domestic Environmental Protection Agency has vigorously promoted the policy of resource utilization of livestock manure. Although this measure has effectively improved its pollution of water bodies and fulfilled the demands of agricultural waste utilization, the commonly used mesophilic and thermophilic anaerobic digestion processes adopted by domestic livestock farmers are not sufficient to effectively reduce the total amount of antibiotic resistance genes (ARGs) in livestock manure. Therefore, the application of biogas slurries and residues as fertilizer in agricultural land may pose risks of promoting the development and dissemination of antibiotic resistance in the environment. Given the limitations of current policies, implementing appropriate post-treatment measures to reduce the spread of antibiotic resistance after the application of biogas slurries and residues as fertilizer on farmland may be a feasible solution. This study proposes a hypothesis that the application of biochar in the soil after the application of biogas slurries and residues as fertilizer may affect the bioavailability of heavy metals and the community changes of soil microorganisms, resulting in a reduction in the spread of ARGs in the soil ecosystem. Furthermore, multiple statistical analyses are conducted to determine the degree and mechanisms of the impact of different biochars on antibiotic resistance in the soil after the application of biogas slurries and residues as irrigation. The experimental results of biochar characterization analysis show that biochar modified with potassium permanganate possesses manganese functional groups that are effectively fixed on the material, confirming the preparation of manganese-modified biochar (M300, M600). The experimental results of different biochar adsorbing Cu(II) and Zn(II) from the aqueous phase indicate that manganese-modified biochar (M300, M600) has a much higher adsorption capacity for both heavy metals compared to conventional biochar (B300, B600), and biochar produced by low-temperature calcination exhibits even stronger adsorption capacity. The maximum adsorption capacities for Cu(II) and Zn(II) reached 136.986 and 133.333 μmol/g, respectively. It is also found that all biochars exhibit chemical adsorption modes for Cu(II) and Zn(II). Subsequently, after conducting a one-month simulated test using different biochars, the analysis of soil environmental parameters reveals a significant increase in total organic carbon (TOC) and total nitrogen (TN) in soil samples treated with biochar. The bioavailable copper (bioCu) content significantly decreased, dropping from 23% to 13% when M300 biochar was added compared to the control group C2. One stewardship gene (16S rRNA gene), three different antibiotic resistance genes (ermB, sul1, tetM), and one mobile genetic element (intI1) were tested, and the results indicated that high-temperature biochars (B600, M600) significantly reduced the abundance of 16S rRNA gene in soil samples with increasing incubation time (p < .05). The results indicate that B600 and M600 biochars likely reduce antibiotic resistance mechanisms in soil after biogas slurry irrigation by decreasing bacterial counts and subsequently reducing ARGs/MGE abundance in the shrinkage test soil
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system. In terms of relative abundance, the statistical results indicate that M300 biochar has a more significant effect on reducing antibiotic resistance in the soil (p < .05), and its mechanism may be related to the fixation of Cu(II) in the soil by M300 biochar, transforming the bioavailable Cu(II) in the soil system into a less accessible form for microorganisms. The correlation analysis and redundancy analysis confirm a strong positive correlation (p < .05) between bioavailable copper content and ARGs/MGEs, further suggesting that the heavy metal Cu(II) in biogas slurries and residues contributes to the abundance of ARGs/MGEs in the soil to some extent. Unfortunately, significant changes in bacterial community composition in the simulated soil due to the application of biochar were not observed in the next-generation sequencing analysis. However, based on the above results, it can be concluded that biochar, specially modified biochar, may reduce antibiotic resistance in the soil after the application of biogas slurries and residues as fertilizer through different mechanisms. | en_US |