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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-132
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-132
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 23 Apr 2019

Submitted as: research article | 23 Apr 2019

Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Biogeosciences (BG).

Major role of ammonia-oxidizing bacteria in N2O production in the Pearl River Estuary

Li Ma1,2, Hua Lin1,2,3, Xiabing Xie1, Minhan Dai1,2, and Yao Zhang1,2 Li Ma et al.
  • 1State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361101, China
  • 2College of Ocean and Earth Sciences, Xiamen University, Xiamen 361101, China
  • 3Key Laboratory of Marine Ecosystem and Biogeochemistry, State Oceanic Administration, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou 310012, China

Abstract. Nitrous oxide (N2O) has significant global warming potential as a greenhouse gas. Estuarine and coastal regimes are the major zones of N2O production in the marine system. However, biological sources of N2O in estuarine ecosystems remains controversial, but is of great importance for understanding the global N2O emission patterns. Here, we measured concentrations and isotopic compositions of N2O as well as distributions and transcript levels of ammonia-oxidizing bacterial and archaeal amoA and denitrifier nirS genes by quantitative polymerase chain reaction along a salinity gradient in the Pearl River Estuary, and performed in situ incubation experiments to estimate N2O yields. Our results indicated that nitrification predominantly occurred, with significant N2O production during ammonia oxidation, in the hypoxic waters of the upper estuary where the maximum N2O and △N2O concentrations were observed, although minor denitrification might be concurrent at the site with the lowest dissolved oxygen. Ammonia-oxidizing β-proteobacteria (AOB) were significantly positively correlated with all N2O parameters, although their amoA gene abundances were distinctly lower than ammonia-oxidizing Archaea (AOA) throughout the estuary. Furthermore, the N2O production rate and the N2O yield normalized to amoA gene copies or transcripts estimated a higher relative contribution of AOB to the N2O production in the upper estuary. Taken together, the in situ incubation experiments, N2O isotopic composition and concentrations, and gene datasets suggested that the high concentration of N2O (oversaturated) is mainly produced from strong nitrification by the relatively high abundance of AOB in the upper reaches as the major source of N2O emitted to the atmosphere in the whole estuary.

Li Ma et al.
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Li Ma et al.
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Short summary
The major microbial process producing N2O in estuarine ecosystems remain controversial. Combining the concentrations and isotopic compositions of N2O, distributions and transcript levels of ammonia-oxidizing bacterial and archaeal amoA and denitrifier nirS genes, and in situ incubation estimates of nitrification rates and N2O production rates, we clarified that ammonia-oxidizing bacteria contributed the major part in N2O production in the upper Pearl River Estuary despite their low abundance.
The major microbial process producing N2O in estuarine ecosystems remain controversial....
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