Keywords: 
• oxytetracycline /
• denitrification /
• fluorescence quantitative /
• T-RFLP

Abstract: Denitrification plays an important role in soil nitrogen cycling. However, there are still few reports on effects of antibiotic residues on denitrification in China. The present study constructed an indoor manure-soil model by adding different concentrations of oxytetracycline. Four groups in different concentrations of oxytetracycline were set up:blank group (0 µg·kg^-1), low concentration group (20 µg·kg^-1), medium concentration group (200 µg·kg^-1), high concentration group (2 000 µg·kg^-1) so as to explore the effect of oxytetracycline on denitrification in soil after chicken manure application. The response of denitrifying genes (nirS, nirK, narG and nosZ) and the denitrifying microbial community were analyzed by Real-time Quantitative (qPCR) and Terminal Restriction Fragment Length Polymorphism (T-RFLP). qPCR results showed that low and medium concentrations of oxytetracycline promoted the abundance of bacteria carrying nirS and nirK genes, whereas the high concentration posed inhibitory effects on these bacteria. The bacteria carrying nosZ gene was less responsive to oxytetracycline stress. T-RFLP results showed that different concentrations of oxytetracycline did not change the dominant bacteria carrying nirS gene and nosZ gene. The dominant denitrification fragment carrying nirS gene had changed between 30 and 60 days in the extension of exposure time. These results indicated that different concentrations of oxytetracycline could affect the abundance of denitrifying bacteria, but could not affect the abundance of dominant bacteria.