Combined effects of chlortetracycline and dissolved organic matter extracted from pig manure on the functional diversity of soil microbial community

Large amounts of tetracyclines (TCs), the most widely used veterinary antibiotics (VAs), can enter agricultural soil via the application of animal manure to land. The effects of VAs on the soil microbial community function are not well understood. Particularly, few works have examined the combinational effects of VAs and dissolved organic matter (DOM) from animal wastes. In this study, DOM was extracted from pig manure and spiked into soils in combination with chlortetracycline (CTC) at three levels (0, 10, 100 mg kg(-1) soil). The control soil received only deionized water, and all treatments were incubated for 1, 6, 12 and 45 days. The microbial community function was characterized by investigating the community level physiological profiles (CLPP) using Biolog EcoPlates(TM) and the activities of several soil enzymes using the spectrophotometry method. The dynamic dissipation of CTC during the incubation period was determined using HPLC. The extractable concentration of CTC was shown to exponentially decrease, and the residual concentration after 45 days was <= 10.8% of the spiking concentration. DOM and CTC had contrary influences on the soil microbial community. The functional diversity indicated by the CLPP and soil enzyme activities were all clearly enhanced by DOM but tended to be inhibited by the co-application of CTC compared to DOM application alone. The significant effect of CTC was deduced to be primarily caused by DOM, which might facilitate bioavailability of CTC and stimulate the activity of microorganisms as additional carbon in the soil. Moreover, all of the microbial parameters were more affected by the incubation time than they were by the DOM and/or CTC treatments. The study demonstrated that the addition of CTC could have a measurable effect on the function of the soil microbial community in the presence of DOM. (C) 2014 Elsevier Ltd. All rights reserved.