Soil HONO emissions at high moisture content are driven by microbial nitrate reduction to nitrite: tackling the HONO puzzle

authored by
Dianming Wu, Marcus A. Horn, Thomas Behrendt, Stefan Müller, Jingsong Li, Jeff A. Cole, Baohua Xie, Xiaotang Ju, Guo Li, Michael Ermel, Robert Oswald, Janine Fröhlich-Nowoisky, Peter Hoor, Chunsheng Hu, Min Liu, Meinrat O. Andreae, Ulrich Pöschl, Yafang Cheng, Hang Su, Ivonne Trebs, Bettina Weber, Matthias Sörgel

Nitrous acid (HONO) is a precursor of the hydroxyl radical (OH), a key oxidant in the degradation of most air pollutants. Field measurements indicate a large unknown source of HONO during the day time. Release of nitrous acid (HONO) from soil has been suggested as a major source of atmospheric HONO. We hypothesize that nitrite produced by biological nitrate reduction in oxygen-limited microzones in wet soils is a source of such HONO. Indeed, we found that various contrasting soil samples emitted HONO at high water-holding capacity (75–140%), demonstrating this to be a widespread phenomenon. Supplemental nitrate stimulated HONO emissions, whereas ethanol (70% v/v) treatment to minimize microbial activities reduced HONO emissions by 80%, suggesting that nitrate-dependent biotic processes are the sources of HONO. High-throughput Illumina sequencing of 16S rRNA as well as functional gene transcripts associated with nitrate and nitrite reduction indicated that HONO emissions from soil samples were associated with nitrate reduction activities of diverse Proteobacteria. Incubation of pure cultures of bacterial nitrate reducers and gene-expression analyses, as well as the analyses of mutant strains deficient in nitrite reductases, showed positive correlations of HONO emissions with the capability of microbes to reduce nitrate to nitrite. Thus, we suggest biological nitrate reduction in oxygen-limited microzones as a hitherto unknown source of atmospheric HONO, affecting biogeochemical nitrogen cycling, atmospheric chemistry, and global modeling.

Institute of Microbiology
External Organisation(s)
East China Normal University
Max Planck Institute for Chemistry (Otto Hahn Institute)
Chinese Academy of Sciences (CAS)
University of Bayreuth
Johannes Gutenberg University Mainz
Anhui University
University of Birmingham
China Agricultural University
King Saud University
Institute of Science and Technology, Luxembourg
The ISME journal
No. of pages
Publication date
Publication status
Peer reviewed
ASJC Scopus subject areas
Microbiology, Ecology, Evolution, Behavior and Systematics
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