Differential response of N2O emissions, N2O-producing and N2O-reducing bacteria to varying tetracycline doses in fertilized soil

Abstract

Tetracyclines are the most widely used antibiotics worldwide. Their presence in soils could affect nutrient cycling, but our knowledge regarding how they affect soil microbial communities involved in greenhouse gas emissions is limited. The objective of the current study was to evaluate how tetracycline is affecting N₂O emissions and the abundance of denitrifiers in fertilized soil. For this purpose, soil mesocosms were treated with only NH₄NO₃ (100 mg/kg) or NH₄NO₃ (100 mg/kg) plus three different doses of tetracycline (0.1, 0.5 and 2 mg/kg). Soils that did not receive tetracycline or NH₄NO₃ were used as controls. Nitrous oxide fluxes were monitored daily for 16 days. The total bacterial (16S rRNA), the abundance of N₂O-reducing and -producing bacteria were quantified by qPCR at the end of the experiment. The application of NH₄NO₃ caused a significant increase of N₂O emissions and AOB abundance but did not affect the abundance of denitrifiers and AOA compared to control soils. Different doses of tetracycline in fertilized soils did not mitigate these N₂O emissions; instead, higher cumulative emissions were noticed in soils treated with the lowest dose. In these soils the total bacterial abundance was higher compared to soils received higher tetracycline concentration. The abundances of the N₂O-producing and N₂O-reducing communities were also differently affected by the addition of tetracycline, which was dose-dependent. Higher doses of tetracycline favored N₂O-reducers within the total bacterial community, which could be important for mitigating N₂O emissions in the long term.

Keywords: Antibiotics; Bacterial community; Nitrogen cycle.