The metabolic intermediate of sulfonamides alters soil nitrous oxide emissions

Veterinary antibiotics are increasingly used in the livestock industry annually. Sulfonamides introduced into the soil with manure are usually largely degraded in various pathways. However, the influence of the metabolic intermediate of sulfonamides on nitrogen (N) cycling under anaerobic conditions in soils has been overlooked. To this end, we carried out a microcosm experiment to investigate the potential consequences of ADPD (2-amino-4,6-dimethylpyrimidine, a degradation product of sulfonamide) at five concentration gradients (i.e., 0, 0.01, 0.1, 1, and 10 mg kg−1) on nitrous oxide (N2O) emissions, associated genes involved in N cycling, antibiotic resistance genes (ARGs), and mobile genetic elements (MGEs) in soils applied with manure or urea. The results showed that ADPD application promoted N2O emissions under flooded conditions at environmentally relevant concentrations, and the maximum cumulative N2O emissions were observed at 1 mg kg−1 and 0.1 mg kg−1 ADPD for manure and urea applied, respectively. The main reasons were the imbalance of denitrifying bacteria, which affected N2O production and reduction, and the increase of antibiotic resistance in soil bacteria. In conclusion, these findings contribute to assessing the eco-environmental risks associated with the prevalence of sulfonamide metabolic intermediates and expand our understanding of the link between antibiotics and N transformation. Further research in the field is warranted to incorporate their recommendations into the greenhouse gas assessment system.