The degradation of soil polycyclic aromatic hydrocarbons (PAHs) under denitrification is one of the most important pathways for anaerobic PAH elimination, but little is known about the effect of nitrate (the terminal electron acceptor for denitrification) on soil denitrification activity and PAH degradation under anaerobic conditions. In this study, the effect of nitrate on soil anthracene anaerobic degradation and denitrification activity was investigated through an anaerobic microcosm experiment. Two groups of treatments without (N0) and with (N30) nitrate (30 mg·kg-1) amendment were conducted. Each group contained three treatments with different anthracene concentrations (0, 15, and 30 mg·kg-1, denoted as A0, A15, and A30, respectively). Therefore, a total of six treatments (N0A0, N0A15, N0A30, N30A0, N30A15, and N30A30) were incubated in darkness at 25℃ for 45 days, and the production rates of N2O and CO2, abundances of denitrification related genes (narG:periplasmic nitrate reductase gene; nirK:copper-containing nitrite reductase gene; and nirS:cd1-nitrite reductase gene), and soil anthracene content were measured at 3, 7, 14, and 45 days. The results indicated that the intensive denitrification enzyme activity in each treatment was only detected at day 3, which could be significantly enhanced by both nitrate and anthracene amendments. Subsequently, a sharp decline of denitrification enzyme activity was observed in each treatment, while anthracene showed an obvious inhibition of soil denitrification enzyme activity. The result of a two-way ANOVA also indicated that nitrate, anthracene, and their interactions had significant effects on soil denitrification enzyme activity. The result of a quantitative-PCR indicated that, during the incubation, the abundances of narG and nirS exhibited an increasing tendency, but the abundance of nirK was relatively constant compared with its former counterparts. The final removal rate of anthracene under anaerobic soil environment was in the range of 33.83%-55.01%, and neither the final removal rate nor the degradation rate of anthracene could be significantly affected by nitrate amendment during incubation. The anthracene degradation rates in the higher anthracene containing treatments (N0A30 and N30A30) were significantly higher than those in the lower anthracene containing treatments (N0A15 and N30A15). In summary, nitrate amendments had no effect on soil anthracene anaerobic degradation but could significantly affect soil denitrification enzyme activity and the abundance of denitrification related narG and nirS genes.
Keywords: anaerobic incubation; anthracene; degradation; denitrification enzyme activity; nitrate; soil.