| dc.description.abstract | The problem of antibiotic resistance has been recognized by the WHO as one of the greatest global public health threats. In addition to medical misuse, antibiotics are often added to animal feed by livestock farmers to both prevent diseases and promote growth of animals. The residual antibiotics and antibiotic resistant bacteria are inevitably excreted to the environment through feces and urine, leading to the problem of antibiotic resistant genes (ARGs) spread in the environment and ultimately the clinic. In recent years, in order to achieving a circular economy effect, our government has actively advocated using anaerobic digestion to treat livestock excrement, converting it into biogas digestate for agricultural use. However, existing literature has pointed out that the commonly used anaerobic digestion processes under ambient-air conditions in Taiwanese livestock farms cannot substantially diminish ARG levels from manure. Previous studies in our research group have also observed the persistence of ARGs in soil after the application of biogas digestate, emphasizing the potential of ARG accumulation in farmland. To address this issue, studies by others have attempted to use biochar to treat ARGs contamination from manure irrigation in farmland and have observed a decrease in ARGs abundance. However, there is still limited research on the use of biochar to treat ARGs contamination in soil receiving biogas digestate. Therefore, in this study, waste mushroom grow bag (M) and rice husk (R) were collected and pyrolyzed at different temperatures (300 ℃ and 600 ℃) to obtain four types of biochar samples (designated as M3, M6, R3, R6). After comparing their properties, the biochar was mixed with soil at a ratio of 2% (w/w). A control group (CK) without biochar addition was also included, resulting in a total of five groups. Pak choi (Brassica rapa chinensis) was planted in pots to simulate the agricultural environment, and the changes in the abundance of four types of ARGs (tetM, sul1, ermB, blaTEM), the class 1 integron gene intI1 (MGE), and the 16S rRNA gene were examined in the bulk and rhizosphere soil over a period of 30 days. The results showed that: (1) The CK group with only pak choi planting significantly reduced the abundance of ARGs/ MGE in the soil within 30 days, but there was a substantive increase on day 30 compared to day 20; (2) The biochar-added groups continuously decreased the abundance of ARGs/MGE on day 30 and generally had significantly lower values than the CK group. However, the abundance of sul1 and intI1, although significantly reduced after treatment, still maintained a certain level, indicating the need for special attention in the future; (3) The mushroom grow bag biochar group showed significantly lower ARGs/MGE abundance than the CK group on day 0, while the rice husk biochar group only showed a slight decrease without significant differences compared to the CK group. Both materials had lower abundance in the 300 ℃ group on day 0. On day 30, the biochar-added groups exhibited different conditions for different genes, but the M3 group consistently had significantly lower relative abundance than the other groups; (4) The assessment of soil ARGs/MGE decay using two models showed similar trends for sul1, intI1, blaTEM, and total ARGs. In the rice husk biochar group, the decay coefficients for sul1, intI1, and total ARGs were higher than those of the mushroom grow bag biochar group, while for blaTEM, the 300 ℃ biochar group had higher decay coefficients than the 600 ℃ biochar group, and the R6 group showed an increase. The mushroom grow bag biochar group consistently had the slowest decay coefficients among the different genes; (5) The addition of biochar significantly altered the microbial community structure in the soil, resulting in different bacterial compositions among the groups, with the M3 group showing the greatest difference compared to the other groups. The microbial communities from the biogas slurry/residue were suppressed by the original microorganisms in the soil, resulting in a significant decrease in the relative abundance of related microbial communities after 30 days; (6) All target ARGs/MGE showed significant positive correlations with each other and significant negative correlations with the 16S rRNA gene. This suggests that as the microbial population increases, bacteria carrying ARGs may incur additional fitness costs, leading to a tendency to discard ARGs. The correlation analysis between ARGs/MGE and environmental factors was limited due to the lack of comprehensive environmental factor measurements, and the redundancy analysis (RDA) had low explanatory power. Future research should conduct more comprehensive analyses to understand the overall impact of environmental factors on ARGs/MGE. | en_US |