LAUSR

Contrary to the fact that NO3−-N can serve as electron acceptor to promote organics degradation, it was also found NO3−-N reduction does not necessarily promote organics degradation. We speculate nitrogen (N) species may control the interaction between NO3−-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 (NO3−-N, NO2−-N, and NH4+-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, NO2−-N inhibited NO3−-N reduction while enhanced aniline degradation. For NH4+-N, it promoted NO3−-N reduction when NH4+-N/NO3−-N concentration ratio ≤ 2 and inhibited aniline degradation when NH4+-N/aniline concentration ratio ≥ 0.5. The presence of NO2−-N or NH4+-N weakened the interaction between NO3−-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 NO2−-N weakened the interaction by affecting both denitrification enzyme activity and electron transfer capability, while NH4+-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 NO3−-N reduction.