EGU General Assembly 2020
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Source-process partitioning of soil N2O and CO2 production: nitrogen and simulated exudate additions

Erin Daly and Guillermo Hernandez Ramirez
Erin Daly and Guillermo Hernandez Ramirez
  • University of Alberta, Renewable Resources, Canada (

Understanding the source partitioning of carbon dioxide (CO2) and nitrous oxide (N2O) fluxes from soil is integral for the characterization of total fluxes and the quantification of potential soil organic matter priming effects. Additionally, we utilized 15N-N2O site preference data to analyze the process priming of microbial nitrification and denitrification on subsequent N2O fluxes. A 32-day laboratory incubation was designed to examine the effects of artificial exudate, nitrogen fertilizer and their potential interactive effects on CO2 and N2O fluxes, soil organic matter source-priming and N2O process-priming. Artificial root exudate (ARE) consisting of a mixture of 99 atom% 13C labelled compounds at three addition rates (0, 6.2, 12.5 mg C kg-1 soil day-1) was applied daily for 21 days to microcosms with or without urea fertilizer, a subset of which was labelled with 5 atom % 15N. Measurements of CO2 and N2O fluxes, isotopic composition and N2O site preference were frequent throughout the duration of the experiment. Source partitioning of CO2 fluxes showed that soil organic carbon (SOM-C) positive priming was significantly altered by additions of artificial exudate and urea (p < 0.001 and 0.001, respectively). When applied concurrently, urea addition had an antagonistic interactive effect on SOM-C sourced CO2 fluxes (p < 0.001).  Source partitioning of N2O flux data revealed that soil organic matter nitrogen (SOM-N) was positively primed for N2O flux by the addition of urea fertilizer (p < 0.001), but positive SOM-N priming was reduced by an antagonistic interaction with artificial exudate application (p < 0.001). Further, examination of 15N-N2O site preference found that the main processes by which N2O is formed (nitrification and denitrification) were differentially process-primed by the addition or absence of ARE. Cumulative denitrification and nitrification contributions to total N2O flux were both positively primed in the soils receiving both ARE and urea inputs relative to a control (50.0 ± 10.1 and 28.2± 8.0 μg N2O-N kg-1, respectively). In soils receiving only ARE application, denitrification-derived N2O was negatively primed relative to a control and thus contributed less to overall N2O flux (-9.5 ± 12.4 μg N2O-N kg-1) but nitrification-derived N2O was positively primed (17.2 ± 9.0 μg N2O-N kg-1).

How to cite: Daly, E. and Hernandez Ramirez, G.: Source-process partitioning of soil N2O and CO2 production: nitrogen and simulated exudate additions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2221,, 2020

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Presentation version 1 – uploaded on 04 Apr 2020
  • AC1: Comment on EGU2020-2221, Guillermo Hernandez-Ramirez, 03 May 2020

    Excellent job synthetizing carbon and nitrogen interacting effects on nitrous oxide and carbon dioxide fluxes and sources. 

  • CC1: Comment on EGU2020-2221, Dominika Lewicka-Szczebak, 04 May 2020

    Hi Erin,

    I wonder how you use 15N-N2O site preference to distinguish nitrification and denitrification? Have you also measured other N2O isotopes (N or O)? Have you taken posible N2O reduction into consideration?

    • AC2: Reply to CC1, Erin Daly, 04 May 2020

      Hello Dominika,

      Thank you very much for your interest.

      Continuous mode quantum cascade laser is used to quantify the mixing ratios of  14N-14N-16O, 14N-15N-16O (α) and 15N-14N-16O (β), and site preference is calculated as a conservative measurement. A two-source mixing model uses SP end members from pure culture studies of N2O formation from nitrifiers (via hydroxylamine oxidation) and dentrifiers (via nitrite reduction), which have distinct site preference values. This leads to determining the proportion of net N2O from each process. Please see the following publication by Toyoda et al. (2011) for more insight into the methodology:

      Our research question revolves around the priming of denitrification and nitrification to source N2O. Our focus is on net N2O as it is a highly potent greenhouse gas of concern.

      • CC3: Reply to AC2, Dominika Lewicka-Szczebak, 06 May 2020

        Hi Erin,

        thanks for your answer.

        Toyoda et al, 2011 applied 2 isotope tracer: 15N-N2O site preference and d15N bulk values to distinguish nitrification and denitrification and also to account for N2O reduction. I think the distinction of these processes based on site preference only and neglecting possible N2O reduction (which is associated with isotope fractionation and changes the site preference signature of initially emitted N2O) is not precise. 

        Another idea is to use site preference data coupled with d18O values to identify both N2O mixing and reduction. Maybe you'd find the papers useful for developing more precise differenciation of nitrification and denitrification: ,



        • AC3: Reply to CC3, Erin Daly, 08 May 2020

          Hello Dominika, 

          Thanks very much for your input, I appreciate all of the important considerations you have provided. I will look into the papers you have suggested. 


  • CC2: Comment on EGU2020-2221, Maria Heiling, 06 May 2020

    Hi Erin,


    thank you for sharing this interesting work. I would like to know where you procure the reference gasses for the N2O measurements. I would need enrichments from 0-3 atom%15N-N2O, ideally with alpha and beta value. Did you measure CO2 and N2O in continous mode?