Nitrogen species control the interaction between NO3--N reduction and aniline degradation and microbial community structure in the oxic-anoxic transition zone

Contrary to the fact that NO 3 − -N can serve as electron acceptor to promote organics degradation, it was also found NO 3 − -N reduction does not necessarily promote organics degradation. We speculate nitrogen (N) species may control the interaction between NO 3 − -N reduction and organics degradation via shifting related microbial community structure. To prove the hypothesis, oxic-anoxic transition zone (OATZ) microcosms simulated by lake water and sediment were conducted with the addition of N species (NO 3 − -N, NO 2 − -N, and NH 4 + -N) and aniline as typical organics. High-throughput sequencing was used to analyze the microbial community structure and functional enzyme in the microcosms. Results show that, NO 2 − -N inhibited NO 3 − -N reduction while enhanced aniline degradation. For NH 4 + -N, it promoted NO 3 − -N reduction when NH 4 + -N/NO 3 − -N concentration ratio ≤ 2 and inhibited aniline degradation when NH 4 + -N/aniline concentration ratio ≥ 0.5. The presence of NO 2 − -N or NH 4 + -N weakened the interaction between NO 3 − -N reduction and aniline degradation, which might be caused by significant changes in the diversity and abundance of microbial communities controlled by N species. The microbial mechanism indicates that NO 2 − -N weakened the interaction by affecting both denitrification enzyme activity and electron transfer capability, while NH 4 + -N weakened the interaction mainly by affecting electron transfer capability. These results imply that N species, as well as other electron acceptors and donors, in the contaminated OATZ should be fully considered, when performing in situ remediation technology of NO 3 − -N reduction.