The large-scale development of animal husbandry and the wide agricultural application of livestock manure lead to more and more serious co-pollution of heavy metals and antibiotics in soil. In this study, two common feed additives, copper (Cu) and sulfadiazine (SDZ), were selected as target pollutants to evaluate the toxicity and interaction of antibiotics and heavy metals on ammonia oxidizers diversity, potential nitrification rate (PNR), and enzymatic activity in black soils. The results showed that soil enzyme activity was significantly inhibited by single Cu pollution, but the toxicity could be reduced by introducing low-concentration SDZ (5 mg · kg-1), which showed an antagonistic effect between Cu and SDZ (5 mg · kg-1), while the combined toxicity of high-concentration SDZ (10 mg · kg-1) and Cu were strengthened compared with the single Cu contamination on soil enzymes. In contrast, soil PNR was more sensitive to single Cu pollution and its combined pollution with SDZ than the enzyme activity. Real-time fluorescence quota PCR and Illumina Hiseq/Miseq sequencing results showed that ammonia-oxidizing archaea (AOA) was decreased in C2 (200 mg · kg-1 Cu treatment) and ammonia-oxidizing bacteria (AOB) was obviously stimulated in soil contaminated in C2, while in S5 (5 mg · kg-1 SDZ treatment), AOB was decreased; both AOA and AOB were significantly decreased at gene level in soils with combined pollutants (C2S5, 200 mg · kg-1 Cu combined with 5 mg · kg-1 SDZ). So, it can be concluded that combined pollution can cause more serious toxicity on the enzymatic activity, PNR, and ammonia-oxidizing microorganisms in soil through the synergistic effect between heavy metals and antibiotics pollutants.
Keywords: AOA; AOB; Combined contamination; Cu; Enzyme activity; SDZ.