Greenhouse gas emissions from riparian zone cropland in a tributary bay of the Three Gorges Reservoir, China

NO3- is an important driver of nitrite-dependent anaerobic methane oxidation bacteria and CH4 fluxes in the reservoir riparian zone

Nitrite-dependent anaerobic methane oxidation (N-DAMO) is an important biological process that combines microbial nitrogen and carbon cycling and is mainly carried out by nitrite-dependent anaerobic methane-oxidizing bacteria. The discovery of this microbial process has changed the conventional view of methane oxidation and nitrogen loss. In this study, the abundance, diversity, and community structure of N-DAMO bacteria were investigated based on high-throughput sequencing and fluorescence quantitative PCR measurements. We examined environmental factors driving the variations of CH₄ fluxes and N-DAMO bacterial using correlation analysis and redundancy analysis. We found low CH₄ fluxes and abundant N-DAMO bacteria in the riparian zone. After decomposing the effects of single variables and exploring them, NO₃^- was the only significant factor that significantly correlated with the abundance and richness of the N-DAMO community and gas fluxes (p < 0.05). Under the influence of three different land use types, the increase in NO₃^- (grassland vs. woodland and sparse woods, + 132.81% and + 106.25%) caused structural changes in the composition of the N-DAMO bacterial community, increasing its abundance (- 9.58% and + 21.19%), thus promoting the oxidation of CH₄ and reduced CH₄ emissions (+ 4.78% and + 35.63%) from the riparian zone. Appropriate NO₃^- input helps maintain the existing low methane emission fluxes in the riparian zone of the reservoir.