Evaluating the role of high N 2 O affinity complete denitrifiers and non-denitrifying N 2 O reducing bacteria in reducing N 2 O emissions in river

• Published in: Journal of hazardous materials Vol. 479; p. 135602
• Main Authors: Yeerken, Senbati, Deng, Min, Li, Lu, Thi Kinh, Co, Wang, Zezheng, Huang, Yongxia, Xiao, Yanlin, Song, Kang
• Format: Journal Article
• Language: English
• Published: Netherlands 24.08.2024
• Subjects: Biokinetic; nosZ; Electron donor; Microbial community; NO flux
• ISSN: 1873-3336

Freshwater rivers are hotspots of N O greenhouse gas emissions. Dissolved organic carbon (DOC) is the dominant electron donor for microbial N O reduction, which can reduce N O emission through enriching high N O affinity denitrifiers or enriching non-denitrifying N O-reducing bacteria (N ORB), but the primary regulatory pathway remains unclear. Here, field study indicated that high DOC concentration in rivers enhanced denitrification rate but reduced N O flux by improving nosZ gene abundance. Then, four N O-fed membrane aeration biofilm reactors inoculated with river sediments from river channel, estuary, adjacent lake, and a mixture were continuously performed for 360 days, including low, high, and mixed DOC stages. During enrichment stages, the (nirS+nirK)/nosZ ratio showed no significant difference, but the community structure of denitrifiers and N ORB changed significantly (p < 0.05). In addition, N ORB strains isolated from different enrichment stages positioned in different branches of the phylogenetic tree. N ORB strains isolated during high DOC stage showed significant higher maximum N O-reducing capability (V : 0.6 ± 0.4 ×10 pmol h cell ) and N O affinity (a : 7.8 ± 7.7 ×1 L cell h ) than strains isolated during low (V : 0.1 ± 0.1 ×10 pmol h cell , a : 0.7 ± 0.4 ×1 L cell h ) and mixed DOC stages (V : 0.1 ± 0.1 ×10 pmol h cell , a : 0.9 ± 0.9 ×1 L cell h ) (p < 0.05). Hence, under high DOC concentration conditions, the primary factor in reducing N O emissions in rivers is the enrichment of complete denitrifiers with high N O affinity, rather than non-denitrifying N ORB.