In:
Biogeosciences, Copernicus GmbH, Vol. 18, No. 3 ( 2021-02-16), p. 1185-1201
Abstract:
Abstract. The prediction of nitrous oxide (N2O) and of dinitrogen (N2)
emissions formed by biotic denitrification in soil is notoriously difficult
due to challenges in capturing co-occurring processes at microscopic scales.
N2O production and reduction depend on the spatial extent of anoxic
conditions in soil, which in turn are a function of oxygen (O2) supply
through diffusion and O2 demand by respiration in the presence of an
alternative electron acceptor (e.g. nitrate). This study aimed to explore controlling factors of complete denitrification
in terms of N2O and (N2O + N2) fluxes in repacked soils by
taking micro-environmental conditions directly into account. This was
achieved by measuring microscale oxygen saturation and estimating the
anaerobic soil volume fraction (ansvf) based on internal air distribution
measured with X-ray computed tomography (X-ray CT). O2 supply and
demand were explored systemically in a full factorial design with soil
organic matter (SOM; 1.2 % and 4.5 %), aggregate size (2–4 and 4–8 mm), and
water saturation (70 %, 83 %, and 95 % water-holding capacity, WHC) as factors. CO2 and N2O
emissions were monitored with gas chromatography. The 15N gas flux
method was used to estimate the N2O reduction to N2. N gas emissions could only be predicted well when explanatory variables for
O2 demand and O2 supply were considered jointly. Combining
CO2 emission and ansvf as proxies for O2 demand and supply resulted in
83 % explained variability in (N2O + N2) emissions and together
with the denitrification product ratio [N2O / (N2O + N2)]
(pr) 81 % in N2O emissions. O2 concentration measured by
microsensors was a poor predictor due to the variability in O2 over
small distances combined with the small measurement volume of the
microsensors. The substitution of predictors by independent, readily
available proxies for O2 demand (SOM) and O2 supply
(diffusivity) reduced the predictive power considerably (60 % and 66 %
for N2O and (N2O+N2) fluxes, respectively). The new approach of using X-ray CT imaging analysis to directly quantify
soil structure in terms of ansvf in combination with N2O and
(N2O + N2) flux measurements opens up new perspectives to estimate
complete denitrification in soil. This will also contribute to improving
N2O flux models and can help to develop mitigation strategies for
N2O fluxes and improve N use efficiency.
Type of Medium:
Online Resource
ISSN:
1726-4189
DOI:
10.5194/bg-18-1185-2021
DOI:
10.5194/bg-18-1185-2021-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2021
detail.hit.zdb_id:
2158181-2
