Nitrogen process in stormwater bioretention: effect of the antecedent dry days on the relative abundance of nitrogen functional genes

In this study, we evaluated the relative abundance of nitrogen functional genes (amoA, nirK and nirS) involved in ammonia oxidation and denitrification bacteria in laboratory-scale bioretention columns in response to environmental factors (e.g., moisture content, pH, soil organic matter, soil nitrogen) under different antecedent dry days (ADDs). We observed a decrease tendency of the relative abundance of ammonia-oxidizing bacteria at first and then increased when increasing ADDs from 1 to 22 day, while the relative abundance of denitrifying bacteria showed a downward trend. The abundance of bacteria gene amoA was positively associated with soil ammonia nitrogen concentration (r2 = 0.389, p < 0.05) and soil organic matter concentration (r2 = 0.334, p < 0.05), while the abundance of bacteria gene nirS was positively correlated with soil ammonia nitrogen (r2 = 0.730, p < 0.01), soil organic matter (r2 = 0.901, p < 0.01) and soil total nitrogen (r2 = 0.779, p < 0.01). Furthermore, gene counts for bacteria gene nirS were correlated negatively with plant root length (r2 = 0.364, p < 0.05) and plant biomass (r2 = 0.381, p < 0.05). Taken together, these results suggest that both nitrification and denitrification can occur in bioretention systems, which can be affected by environmental factors.