scholarly journals Application of the <sup>15</sup>N-Gas Flux method for measuring in situ N<sub>2</sub> and N<sub>2</sub>O fluxes due to denitrification in natural and semi-natural terrestrial ecosystems and comparison with the acetylene inhibition technique

2015 ◽  
Vol 12 (15) ◽  
pp. 12653-12689 ◽  
Author(s):  
F. Sgouridis ◽  
S. Ullah ◽  
A. Stott
Keyword(s):  
Gas Injection ◽  
Terrestrial Ecosystems ◽  
15N Tracer ◽  
Organic Soils ◽  
Acetylene Inhibition ◽  
Flux Method ◽  
Gas Flux ◽  
Acetylene Inhibition Technique ◽  
Inhibition Technique

Abstract. Soil denitrification is considered the most un-constrained process in the global N cycle due to uncertain in situ N2 flux measurements, particularly in natural and semi-natural terrestrial ecosystems. 15N tracer approaches can provide in situ measurements of both N2 and N2O simultaneously, but their use has been limited to fertilised agro-ecosystems due to the need for large 15N additions in order to detect 15N2 production against the high atmospheric N2. For 15N-N2 analyses, we have used an "in house" laboratory designed and manufactured N2 preparation instrument which can be interfaced to any commercial continuous flow isotope ratio mass spectrometer (CF-IRMS). The N2 prep unit has gas purification steps, a copper based reduction furnace, and allows the analysis of small gas injection volumes (4 μL) for 15N-N2 analysis. For the analysis of N2O, an automated Tracegas Pre-concentrator (Isoprime Ltd) coupled to an IRMS was used to measure the 15N-N2O (4 mL gas injection volume). Consequently, the coefficient of variation for the determination of isotope ratios for N2 in air and in standard N2O (0.5 ppm) was better than 0.5 %. The 15N Gas-Flux method was adapted for application in natural and semi-natural land use types (peatlands, forests and grasslands) by lowering the 15N tracer application rate to 0.04–0.5 kg 15N ha−1. For our chamber design (volume / surface = 8:1) and a 20 h incubation period, the minimum detectable flux rates were 4 μg N m−2 h−1 and 0.2 ng N m−2 h−1 for the N2 and N2O fluxes respectively. The N2 flux ranged between 2.4 and 416.6 μg N m−2 h−1, and the grassland soils showed on average 3 and 14 times higher denitrification rates than the woodland and organic soils respectively. The N2O flux was on average 20 to 200 times lower than the N2 flux, while the denitrification product ratio (N2O/N2 + N2O) was low, ranging between 0.03 and 13 %. Total denitrification rates measured by the acetylene inhibition technique under the same field conditions correlated (r = 0.58) with the denitrification rates measured under the 15N Gas-Flux method but were underestimated by a factor of 4 and this was attributed to the incomplete inhibition of N2O reduction to N2 under relatively high soil moisture content. The results show that the 15N Gas-Flux method can be used for quantifying N2 and N2O production rates in natural terrestrial ecosystems, thus significantly improving our ability to constrain ecosystem N budgets.

scholarly journals Application of the <sup>15</sup>N gas-flux method for measuring in situ N<sub>2</sub> and N<sub>2</sub>O fluxes due to denitrification in natural and semi-natural terrestrial ecosystems and comparison with the acetylene inhibition technique

2016 ◽  
Vol 13 (6) ◽  
pp. 1821-1835 ◽  
Author(s):  
Fotis Sgouridis ◽  
Andrew Stott ◽  
Sami Ullah
Keyword(s):  
Terrestrial Ecosystems ◽  
15N Tracer ◽  
Acetylene Inhibition ◽  
Flux Method ◽  
Gas Flux ◽  
Acetylene Inhibition Technique ◽  
Land Use Types ◽  
N2o Fluxes ◽  
Inhibition Technique

Abstract. Soil denitrification is considered the most un-constrained process in the global N cycle due to uncertain in situ N2 flux measurements, particularly in natural and semi-natural terrestrial ecosystems. 15N tracer approaches can provide in situ measurements of both N2 and N2O simultaneously, but their use has been limited to fertilized agro-ecosystems due to the need for large 15N additions in order to detect 15N2 production against the high atmospheric N2. For 15N–N2 analyses, we have used an “in-house” laboratory designed and manufactured N2 preparation instrument which can be interfaced to any commercial continuous flow isotope ratio mass spectrometer (CF-IRMS). The N2 prep unit has gas purification steps and a copper-based reduction furnace, and allows the analysis of small gas injection volumes (4 µL) for 15N–N2 analysis. For the analysis of N2O, an automated Tracegas Preconcentrator (Isoprime Ltd) coupled to an IRMS was used to measure the 15N–N2O (4 mL gas injection volume). Consequently, the coefficient of variation for the determination of isotope ratios for N2 in air and in standard N2O (0.5 ppm) was better than 0.5 %. The 15N gas-flux method was adapted for application in natural and semi-natural land use types (peatlands, forests, and grasslands) by lowering the 15N tracer application rate to 0.04–0.5 kg 15N ha−1. The minimum detectable flux rates were 4 µg N m−2 h−1 and 0.2 ng N m−2 h−1 for the N2 and N2O fluxes respectively. Total denitrification rates measured by the acetylene inhibition technique in the same land use types correlated (r =  0.58) with the denitrification rates measured under the 15N gas-flux method, but were underestimated by a factor of 4, and this was partially attributed to the incomplete inhibition of N2O reduction to N2, under a relatively high soil moisture content, and/or the catalytic NO decomposition in the presence of acetylene. Even though relatively robust for in situ denitrification measurements, methodological uncertainties still exist in the estimation of N2 and N2O fluxes with the 15N gas-flux method due to issues related to non-homogenous distribution of the added tracer and subsoil gas diffusion using open-bottom chambers, particularly during longer incubation duration. Despite these uncertainties, the 15N gas-flux method constitutes a more reliable field technique for large-scale quantification of N2 and N2O fluxes in natural terrestrial ecosystems, thus significantly improving our ability to constrain ecosystem N budgets.

Improvement of the 15 N gas flux method for in situ measurement of soil denitrification and its product stoichiometry

2019 ◽  
Vol 33 (5) ◽  
pp. 437-448 ◽  
Author(s):  
Reinhard Well ◽  
Stefan Burkart ◽  
Anette Giesemann ◽  
Balázs Grosz ◽  
Jan Reent Köster ◽  
...  
Keyword(s):  
In Situ Measurement ◽  
Flux Method ◽  
Gas Flux

Effects of nitrate and water content on acetylene inhibition technique bias when analysing soil denitrification rates under an aerobic atmosphere

Geoderma ◽  
2019 ◽  
Vol 334 ◽  
pp. 33-36 ◽  
Author(s):  
Haijing Yuan ◽  
Zhijun Zhang ◽  
Shuping Qin ◽  
Shungui Zhou ◽  
Chunsheng Hu ◽  
...  
Keyword(s):  
Water Content ◽  
Acetylene Inhibition ◽  
Acetylene Inhibition Technique ◽  
Inhibition Technique

Quantifying soil denitrification in situ from depth profiles of 15N labelled denitrification products by diffusion-reaction modelling 

2021 ◽  
Author(s):  
Reinhard Well ◽  
Dominika Lewicka-Szczebak ◽  
Martin Maier ◽  
Amanda Matson
Keyword(s):  
Soil Gas ◽  
Diffusion Reaction ◽  
Flux Method ◽  
Closed Chamber ◽  
Gas Flux ◽  
Depth Profiles ◽  
Chamber Method ◽  
Chamber Measurements ◽  
Closed Chamber Method

&lt;p&gt;Common field methods for measuring soil denitrification in situ include monitoring the accumulation of &lt;sup&gt;15&lt;/sup&gt;N labelled N&lt;sub&gt;2&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O evolved from &lt;sup&gt;15&lt;/sup&gt;N labelled soil nitrate pool in soil surface chambers. Bias of denitrification rates derived from chamber measurements results from subsoil diffusion of &lt;sup&gt;15&lt;/sup&gt;N labelled denitrification products, but this can be corrected by diffusion modeling (Well et al., 2019). Moreover, precision of the conventional &lt;sup&gt;15&lt;/sup&gt;N gas flux method is low due to the high N&lt;sub&gt;2&lt;/sub&gt; background of the atmosphere. An alternative to the closed chamber method is to use concentration gradients of soil gas to quantify their fluxes (Maier &amp;&amp;#160; Schack-Kirchner, 2014). Advantages compared to the closed &amp;#160;chamber method include the facts that (i) time consuming work with closed chambers is replaced by easier sampling of soil gas probes, (ii) depth profiles yield not only the surface flux but also information on the depth distribution of gas production and (iii) soil gas concentrations are higher than chamber gas concentration, resulting in better detectability of &lt;sup&gt;15&lt;/sup&gt;N-labelled denitrification products. Here we use this approach for the first time to evaluate denitrification rates derived from depth profiles of &lt;sup&gt;15&lt;/sup&gt;N labelled N&lt;sub&gt;2&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O in the field by closed chamber measurements published previously (Lewicka-Szczebak et al., 2020).&lt;/p&gt;&lt;p&gt;We compared surface fluxes of N&lt;sub&gt;2&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O from &lt;sup&gt;15&lt;/sup&gt;N labelled microplots using the closed chamber method. Diffusion&amp;#8211;based soil gas probes (Schack-Kirchner et al., 1993) were used to sample soil air at the end of each closed chamber measurement. A diffusion-reaction model (Maier et al., 2017) will be &amp;#160;used to fit measured and modelled concentrations of &lt;sup&gt;15&lt;/sup&gt;N labelled N&lt;sub&gt;2&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O. Depth-specific values of denitrification rates and the denitrification product ratio will be obtained from best fits of depth profiles and chamber accumulation, taking into account diffusion of labelled denitrification products to the subsoil (Well et al., 2019).&lt;/p&gt;&lt;p&gt;Depending on the outcome of this evaluation, the gradient method could be used for continuous monitoring of denitrification in the field based on soil gas probe sampling. This could replace or enhance current approaches by improving the detection limit, facilitating sampling and delivering information on depth-specific denitrification. &amp;#160;&lt;/p&gt;&lt;p&gt;References:&lt;/p&gt;&lt;p&gt;Lewicka-Szczebak D, Lewicki MP, Well R (2020) N2O isotope approaches for source partitioning of N2O production and estimation of N2O reduction &amp;#8211; validation with the 15N gas-flux method in laboratory and field studies. Biogeosciences, &lt;strong&gt;17&lt;/strong&gt;, 5513-5537.&lt;/p&gt;&lt;p&gt;Maier M, Longdoz B, Laemmel T, Schack-Kirchner H, Lang F (2017) 2D profiles of CO2, CH4, N2O and gas diffusivity in a well aerated soil: measurement and Finite Element Modeling. Agricultural and Forest Meteorology, &lt;strong&gt;247&lt;/strong&gt;, 21-33.&lt;/p&gt;&lt;p&gt;Maier M, Schack-Kirchner H (2014) Using the gradient method to determine soil gas flux: A review. Agricultural and Forest Meteorology, &lt;strong&gt;192&lt;/strong&gt;, 78-95.&lt;/p&gt;&lt;p&gt;Schack-Kirchner H, Hildebrand EE, Wilpert KV (1993) Ein konvektionsfreies Sammelsystem f&amp;#252;r Bodenluft. Zeitschrift Fur Pflanzenernahrung Und Bodenkunde, &lt;strong&gt;156&lt;/strong&gt;, 307-310.&lt;/p&gt;&lt;p&gt;Well R, Maier M, Lewicka-Szczebak D, Koster JR, Ruoss N (2019) Underestimation of denitrification rates from field application of the N-15 gas flux method and its correction by gas diffusion modelling. Biogeosciences, &lt;strong&gt;16&lt;/strong&gt;, 2233-2246.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

scholarly journals <sup>15</sup>N gas-flux method to determine N<sub>2</sub> emission and N<sub>2</sub>O pathways: a comparison of different tracer addition approaches

2019 ◽  
Author(s):  
Dominika Lewicka-Szczebak ◽  
Reinhard Well
Keyword(s):  
15N Tracer ◽  
Homogeneous Distribution ◽  
Soil Cores ◽  
Flux Method ◽  
Gas Flux ◽  
N Transformations ◽  
Tracer Solution ◽  
Comparison Of The Results ◽  
Label Distribution ◽  
Intact Soil

Abstract. 15N gas flux method allows for quantification of N2 flux and tracing soil N transformations. An important requirement for this method is a homogeneous distribution of the 15N tracer added to soil. This is usually achieved by soil homogenization and admixture of the 15N tracer solution or multipoint injection of tracer solution to intact soil. Both methods may create artefacts. We aimed at comparing the results of the gas flux method using both tracer distribution approaches. Intact soil cores with injected 15N tracer solution show wider range of the results obtained. Homogenized soil shows better agreement between repetitions, but significant differences in 15N enrichment measured in soil nitrate and in emitted gases were also observed. For intact soil the wider variability of measured values rather results from natural diversity of non-homogenized soil cores than from inhomogeneous label distribution. Generally, comparison of the results of intact cores and homogenized soil did not reveal statistically significant differences in N2 flux determination. In both cases, pronounced dominance of N2 flux over N2O flux was noted. It can be concluded that both methods showed close agreement and homogenized soil is not necessarily characterized by more homogenous 15N label distribution.

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