Low nitrogen in biogas slurry application mitigates antibiotic resistance genes in soil

Agricultural soils treated with biogas slurry (BS) have been extensively recognized as hotspots for the development of antibiotic resistance genes (ARGs). The application of BS has been demonstrated to significantly elevate the levels of ARGs in soil. However, there remains a limited understanding of how different nitrogen contents within BS affect ARG profiles. The objectives of this study were to explore the changes in ARGs in soil, as well as the potential mechanisms between BS application dosages and ARG patterns through Illumina sequencing and high-throughput quantitative PCR under five amounts of BS application according to the nitrogen contents. Results indicated that no significant alterations were noticed in the abundance of ARGs under low BS applications (0-120 kg N ha -1 ) comparing to S0, and bacterial networks with different network hubs indicated that significant relationships occurred at high BS treatment (180 kg N ha -1 ), as well as the highest abundance of ARGs and bacterial abundance observed. However, when the BS application at 240 kg N ha -1 which the soil under saturated conditions, the abundance of ARGs decreased in response to a decrease in bacterial number comparing to 180 kg N ha -1 . Structural equation models indicated that the content of NH 4 + -N in soil was the direct driving factor influencing ARG characterizations in BS-amended soil. In summary, low nitrogen contents within BS (under 180 kg N ha -1 ) reduced the increase of ARGs in soil, high nitrogen contents (180-240 kg N ha -1 ) could directly elevate the abundance of ARGs through the introduction of amended nitrogen, disinfection effect of BS played a key role in the decrease of ARGs under anaerobic environments (above 240 kg N ha -1 ). These findings enhanced our understanding of BS application with different nitrogen contents on ARGs in soil, with significant environmental implications for the precise application of BS and high value utilization.