Denitrification potentials in soils are only marginally impacted by distance to air-filled macropores

Denitrification is the sequential reduction of nitrate to dinitrogen. The greenhouse gas nitrous oxide (N₂O) is thereby produced as an intermediate and denitrifiers are thus recognized as a major source N₂O in soils. Denitrification is stimulated by organic carbon, oxygen limitation and nitrate availability. Such edaphic factors are spatially variable in soils and impacted by soil pores. Thus, we addressed the question, whether denitrifiers exhibit spatial patterns relative to variations in distance to soil pores. Undisturbed soil cores were extracted from two agricultural model soils and subsamples of known distance to soil macropores were extracted by the help of an X-ray computed tomography guided strategy. Spatial variability of genetic and process level denitrification potentials was generally high with a minimal impact of pore distance. A minor increase of process level denitrification potentials with distance to pores was observed for one of the soils only. Quantification of genetic denitrification potentials after short incubations were not significantly different among samples. The minor impact of macropore distance on genetic and process-level denitrification potentials suggests that macropores are not the major source of spatial heterogeneity impacting denitrifiers in soils, implying that there is no need to explicitly consider such a parameter for modelling denitrification in soils.