Effects of herbicide mixtures on the diversity and composition of microbial community and nitrogen cycling function on agricultural soil: A field experiment in Northeast China.

Herbicide mixtures application is a widespread and effective practice in modern agriculture; however, a knowledge gap exists regarding the potential ecotoxicological effects of herbicide mixtures in agricultural systems. Here, the effects of various doses of herbicide mixtures (atrazine, nicosulfuron, and mesotrione) under different varieties of maize cultivation on the structure and function of microbial communities and soil chemical parameters were clarified through field experiments. The results showed that the application of herbicide mixtures increased the bacterial and fungal community alpha diversity at jointing and maturity, indicating a prolonged effect of the herbicide mixtures. Moreover, herbicide mixtures alter the composition of bacterial and fungal communities, with sensitive taxa suppressed and herbicide-tolerant taxa enriched. The herbicide mixtures significantly reduced the abundances of Bacillus even at lower doses, but Penicillum was enriched. FAPROTAX analysis and quantitative PCR (qPCR) results showed that herbicide mixtures inhibited the soil nitrogen-cycle process and related genes AOA-amoA, AOB-amoA, and nifH at maize seedling stage. Moreover, network analysis showed that low concentrations of the herbicide mixtures increased bacterial interactions while high concentrations inhibited them, which indicated that the network complexity may be herbicide concentration dependent. A synthetic community (SynCom) consisting of six bacterial strains was established for the biodegradation of the herbicide mixtures based on the analysis of the bacterial network, which resulted in an increase in the degradation efficiency of nicosulfuron by 15.90%. Moreover, potted maize experiment showed that the addition of the SynCom alleviated the toxic effects of herbicide mixtures on the plants. In summary, this study provides a comprehensive perspective for assessing the ecological risk at taxonomic and functional levels and the biodegradation approach of herbicide mixtures residue on agricultural soils in Northeastern China.