Particle-associated denitrification is the primary source of N2O in oxic coastal waters
Xianhui Wan, Huaxia Sheng, Li Liu, Hui Shen, Weiyi Tang, Wenbin Zou, Min Xu, Zhenzhen Zheng, Ehui Tan, Mingming Chen, Yao Zhang, Bess B. Ward, Shuh‐Ji Kao
Abstract
Abstract The heavily human-perturbed coastal oceans are hotspots of nitrous oxide (N 2 O) emission to the atmosphere. The processes underpinning the N 2 O flux, however, remain poorly understood, leading to large uncertainties in assessing global N 2 O budgets. Using a suite of nitrogen isotope labeling experiments, we show that multiple processes contribute to N 2 O production throughout the estuarine-coastal gradient, sustaining intensive N 2 O flux to the atmosphere. Unexpectedly, denitrification, rather than ammonia oxidation as previously assumed, constitutes the major source of N 2 O in well-oxygenated coastal waters. Size-fractionated manipulation experiments with gene analysis further reveal niche partitioning of ammonia oxidizers and denitrifiers across the particle size spectrum; denitrification dominated on large particles and ammonia oxidizers on small particles. Total N 2 O production rate increases with substrate and particle concentrations, suggesting a crucial interplay between nutrients and particles in controlling N 2 O production. The controlling factors identified here may help understand climate feedback mechanisms between human activity and coastal oceans.