EGU2020-5257
https://doi.org/10.5194/egusphere-egu2020-5257
EGU General Assembly 2020
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Oxygen supply and demand as controls of denitrification at the microscale in repacked soil

Lena Rohe1, Steffen Schlüter1, Bernd Apelt1, Hans-Jörg Vogel1, and Reinhard Well2
Lena Rohe et al.
  • 1Helmholtz Centre for Environmental Research - UFZ, Department Soil System Sciences, Leipzig, Germany
  • 2Institute of Climate-Smart Agriculture, von-Thünen-Institute, Braunschweig, Germany

The controlling factors of biotic denitrification in soil as a source of the greenhouse gas nitrous oxide (N2O) and of dinitrogen (N2) are still not fully understood due to the challenges in observing processes that co-occur in soil at microscopic scales and the difficulty to measure N2 fluxes. N2O production and reduction depend on the extent of anoxic conditions in soil, which in turn are a function of O2 supply through diffusion and O2 demand by soil respiration in the presence of an alternative electron acceptor (e.g. nitrate).

This study aimed to explore microscopic drivers that control total denitrification, i.e. N2O and (N2O+N2) fluxes. To provoke different levels of oxygen supply and demand, repacked soils from two locations in Germany were incubated in a full factorial design with soil organic matter (1.2 and 4.5 %), aggregate size (2-4 and 4-8mm) and water saturation (70%, 83% and 95% WHC) as factors. The sieved soils were repacked and incubated at constant temperature and moisture and gas emissions (CO2 and N2O) were monitored with gas chromatography. The 15N tracer application was used to estimate the N2O reduction to N2. The internal soil structure and air distribution was measured with X-ray computed tomography (X-ray CT).

The interplay of anaerobic soil volume fraction (ansvf) as an abiotic proxy of oxygen supply and CO2 emission as a biotic proxy of oxygen demand resulted in 81% and 84% explained variability in N2O and (N2O+N2) emissions, respectively. These high values dropped to 5-30% when only ansvf or CO2 was considered indicating strong interaction effects. The extent of N2O reduction in combination with ansvf and CO2 even increased the explained variability for N2O fluxes to 83%. Average O2 concentration measured by microsensors was a very poor predictor due to the extreme variability in O2 at short scales in combination with the small footprint of the micro sensors probing only 0.2% of the entire soil volume. The substitution of predictors by independent, readily available proxies for O2 supply (diffusivity based on air content) and O2 demand (SOM) leads to a reduction in predictive power.

To our knowledge this is the first study analyzing total denitrification in combination with X-ray CT image analysis, which opens up new perspectives to estimate denitrification in soil and also contribute to improving models of N2O fluxes and fertiliser loss at all scales and can help to develop mitigation strategies for N2O fluxes and improve N use efficiency.

How to cite: Rohe, L., Schlüter, S., Apelt, B., Vogel, H.-J., and Well, R.: Oxygen supply and demand as controls of denitrification at the microscale in repacked soil , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5257, https://doi.org/10.5194/egusphere-egu2020-5257, 2020.

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