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Ammonia oxidation pathways and nitrifier denitrification are significant sources of N2O and NO under low oxygen availability

The continuous increase of nitrous oxide (N2O) abundance in the atmosphere is a global concern. Multiple pathways of N2O production occur in soil, but their significance and dependence on oxygen (O2) availability and nitrogen (N) fertilizer source are poorly understood.

Xia Zhua,b,c,1, Martin Burgerb,1, Timothy A. Doaneb, and William R. Horwathb,1

 

Author Affiliations

 

            1.aCenter for Ecological Studies, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, China;
            2.bBiogeochemistry and Nutrient Cycling Laboratory, Department of Land, Air and Water Resources, University of California, Davis, CA 95616; and
            3.cUniversity of Chinese Academy of Sciences, Beijing 100049, China

 
1.Edited by Mark H. Thiemens, University of California at San Diego, La Jolla, CA, and approved March 8, 2013 (received for review November 16, 2012)

 

Abstract

 

The continuous increase of nitrous oxide (N2O) abundance in the atmosphere is a global concern. Multiple pathways of N2O production occur in soil, but their significance and dependence on oxygen (O2) availability and nitrogen (N) fertilizer source are poorly understood. We examined N2O and nitric oxide (NO) production under 21%, 3%, 1%, 0.5%, and 0% (vol/vol) O2 concentrations following urea or ammonium sulfate [(NH4)2SO4] additions in loam, clay loam, and sandy loam soils that also contained ample nitrate. The contribution of the ammonia (NH3) oxidation pathways (nitrifier nitrification, nitrifier denitrification, and nitrification-coupled denitrification) and heterotrophic denitrification (HD) to N2O production was determined in 36-h incubations in microcosms by 15N-18O isotope and NH3 oxidation inhibition (by 0.01% acetylene) methods. Nitrous oxide and NO production via NH3 oxidation pathways increased as O2 concentrations decreased from 21% to 0.5%. At low (0.5% and 3%) O2 concentrations, nitrifier denitrification contributed between 34% and 66%, and HD between 34% and 50% of total N2O production. Heterotrophic denitrification was responsible for all N2O production at 0% O2. Nitrifier denitrification was the main source of N2O production from ammonical fertilizer under low O2 concentrations with urea producing more N2O than (NH4)2SO4 additions. These findings challenge established thought attributing N2O emissions from soils with high water content to HD due to presumably low O2 availability. Our results imply that management practices that increase soil aeration, e.g., reducing compaction and enhancing soil structure, together with careful selection of fertilizer sources and/or nitrification inhibitors, could decrease N2O production in agricultural soils.

 

http://www.pnas.org/content/110/16/6328.abstract.html?etoc

PNAS April 16, 2013 vol. 110 no. 16 6328-6333

 

 

 

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