Marine ammonia-oxidizing archaea link ocean nitrogen cycling to nitrous oxide emissions in a changing climate
image: Conceptual model showing the major microbial pathways contributing to N2O production in marine environments, including nitrification, denitrification, nitrifier-denitrification, coupled nitrification-denitrification, dissimilatory nitrate reduction to ammonium, and chemodenitrification.
Credit: ©Science China Press
Nitrous oxide (N2O) is a potent and long-lived greenhouse gas, and the ocean is an important natural source of atmospheric N2O. More than 80% of N2O production in the global ocean has been associated with ammonia oxidation, a process predominantly driven by ammonia-oxidizing archaea (AOA) in many marine environments. However, the metabolic pathways through which marine AOA produce N2O and their responses to environmental change remain incompletely understood.
A review by Yihui Guo, Ziya Lin, Xiao Ma, Shuh-Ji Kao, Chuanlun Zhang, and Wei Xie systematically summarizes current understanding of marine AOA-derived N2O production. The authors review the major biogeochemical sources of marine N2O and examine several potential pathways of N2O formation by AOA involving key intermediates such as hydroxylamine (NH2OH), nitroxyl (HNO), and nitric oxide (NO). Although recent isotope-labeling and biochemical studies have provided new evidence for these pathways, the complete metabolic network and key enzymes responsible for N2O formation in AOA remain unresolved.
The review further evaluates how dissolved oxygen, temperature, substrate availability, salinity, light, organic carbon, and pH regulate AOA metabolism and associated N2O production. In particular, low-oxygen conditions may alter electron transport and metabolic fluxes in AOA, while ocean warming can interact with deoxygenation by reducing oxygen solubility and strengthening water-column stratification. Ocean acidification can also change substrate availability for AOA, yet reduced nitrification does not necessarily result in lower N2O production. These responses become more complex when warming, acidification, deoxygenation, and nutrient inputs occur simultaneously.
The authors emphasize that future studies should move beyond single-factor experiments and investigate how multiple environmental drivers jointly regulate AOA-derived N2O production. Combining isotope tracing, in situ incubation, multi-omics approaches, and targeted enzymatic validation will help connect microbial metabolic mechanisms with marine N2O fluxes. A better understanding of these processes could improve predictions of future oceanic N2O emissions and the representation of marine nitrogen cycling in biogeochemical and climate models.
See the article:
Guo Y, Lin Z, Ma X, Kao S J, Zhang C, Xie W. 2026. A hidden driver of the greenhouse effect: Production mechanisms and climate implications of N2O derived from marine planktonic ammonia-oxidizing archaea. Science China Earth Sciences, 69(8): 2839–2855. https://doi.org/10.1007/s11430-025-1940-9