Effects of different concentrations and application frequencies of oxytetracycline on soil enzyme activities and microbial community diversity

Abstract

Antibiotics in soil can interfere with the structure and function of the soil microbial community and represent a potential genetic pollution risk. The effects of different concentrations and application frequencies of oxytetracycline (OTC) to an agricultural soil on the activities of soil microorganisms and enzymes were investigated during incubation of 120 days. Single once-only high application treatments (1, 3.6, 10, and 30 mg OTC kg−1 soil) and one daily low application treatment (0.03 mg OTC kg−1 soil every day) were compared to simulate OTC application to the soil in sewage sludges or manures or from waste water irrigation. In the single addition treatments, microbial biomass carbon (Cmic) in the soil increased 2.17–3.29 times and 1.37–2.08 times after 7 and 42 d of incubation, respectively, but nitrification potential increased sharply to 3.01–10.9 times after 28 d and dehydrogenase activity was also significantly stimulated after 14 d compared to the zero OTC control and decreased sharply by 120 d. The daily OTC addition treatments promoted Cmic (up to 2.64 times) and increased the McIntosh index (p < 0.05) between 60 and 90 days as calculated using Biolog data and compared to the zero OTC control. A single high rate of OTC addition showed a generally more pronounced negative effect on soil microbial community metabolism (but not on functional diversity indices of the soil microbial community) than repeated small rates of addition because with equal amounts of added OTC (single 3.6 mg kg−1 and daily 0.03 mg kg−1 OTC) Cmic, nitrification potential and neutral phosphatase activity at 120 d were significantly lower in the single application treatments.