Liu Yuan, Zhongyang Li*

Institute of Farmland Irrigation, Chinese Academy of Agricultural Sciences, Xinxiang 453002, China

Antibiotic Resistance Genes (ARGs), a kind of contaminants of emerging concern, often occur in the reclaimed water discharged from urban sewage treatment plants and the livestock wastewater. Hence, whether the use of these unconventional waters for irrigation affects the spread of ARGs in soil has become a public concern. However, the existing research conclusions are conflicting. Our results showed that the increasing effect of livestock wastewater on soil antibiotics and their resistance genes was significantly greater than that of reclaimed water. Compared with traditional furrow irrigation, alternate furrow irrigation could significantly reduce the abundance of soil ARGs, and the abundance of rhizosphere ARGs could be reduced by adjusting the irrigation amount of livestock wastewater with alternate furrow irrigation. The change of pH, as well as the coexistence of small molecular organic acids and anions significantly reduced the adsorption of antibiotics by roots. The soybean roots performed strong adsorption ability compared with the maize and wheat roots driven by the variations in root electrochemical properties. Biochar addition did not significantly affect the abundance of soil ARGs under reclaimed water irrigation, while significantly decreased the abundance of soil ARGs under livestock wastewater irrigation. We also found that even after 16 years of irrigation, the cropping system but not the reclaimed water irrigation had a consistent influence, at a significant level, upon the assemblages of insertion sequences and genes conferring resistance to antibiotics, metals, and biocides. Long-term application of farmyard manure to arable soils does not, in itself, promote the spread of antibiotic resistance genes. These findings provide a theoretical basis for the safe utilization of reclaimed water and livestock wastewater, and highlight the significance of crop management in mitigating dissemination of ARGs.