Coordination Funds

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Denitrification, the process of nitrate reduction allowing microbes to sustain respiration under anaerobic conditions, is the key process returning reactive nitrogen as N2 to the atmosphere. The different reaction steps (NO3- ->NO2- ->NO ->N2O->N2) are enzymatically mediated by a broad range of prokaryotes and some eukaryotes. Despite being intensively studied for more than 100 years, denitrification rates and emissions of its gaseous products can still not be satisfactorily predicted. In DASIM phase I we have focused on investigations under laboratory conditions ranging from very simple systems such as glass beads to re-packed soil columns with and without hot spots. Three typical mid-European agricultural soils were selected, characterized and used to carry out denitrification studies. A focus was on the identification of processes responsible for N2O and N2 production via the use of stable isotope tracing methods (15N and 18O) in combination with advanced microbial, soil physical and soil chemical (e.g. organic matter) investigations. Moreover, investigation into the soil microsite structure were carried out via µCT in combination with high-resolution 3D modelling. In DASIM phase II the investigations will move to more realistic systems such as intact soil cores and field investigations and in particular the influence of plants (e.g. exudation pattern) on denitrification in the rhizosphere. New advanced techniques to measure N2 emissions will be applied such as a method where N2 is quantified under a reduced N2 atmosphere or Raman spectroscopy where N2 can directly be quantified. Based on the small-scale measurements, upscaling functions will be developed so that the information gained via the detailed soil structural identification can also be included and tested in ecosystems models, in particular LandscapeDNDC. The final aim is to obtain an improved understanding on denitrification and the processes associated with N2O and N2 production and their prediction with numerical models which provides important information to derive suitable mitigation techniques.