The impact of the nitrification inhibitor DMPP on agricultural soil microbial communities

Agricultural soils contribute as major polluters of nitrous oxide (N₂O) emissions in Europe, which are a result of microbial nitrification and denitrification processes. Nitrification inhibitors (NI) have gained attention by decreasing N₂O emissions and nitrate leaching, thereby promoting the uptake of nitrogen (N) by plants. However, concerns have been raised about the long-term efficiency of NI at the scale of microbial communities, for example if taxa develop resistance. This work hypothesises that target and non-target microbial taxa develop resistance to NIs over time after showing initial sensitivity to 3,4-Dimethylpyrazole phosphate (DMPP) application. More in depth, specific nitrifying organisms will be less resilient against DMPP in an agricultural field with a high clay/sand ratio. Lastly, different types of fertilizations interact differently with DMPP, creating a change in the response of Ammonia oxidizing bacteria and archaea gene abundance.

The study was conducted on agricultural fields located in Köningslutter, Lower Saxony (Silt loam) and Hohenhiem, Baden-Wuerttemberg (Silty clay loam). One of three distinct fertilizers was applied to each field, specifically ammonium sulphate nitrate, slurry or urea ammonium nitrate solution, in combination with or without DMPP. Samples were taken at four different time points over the growing season of winter wheat. Additional physicochemical parameters including N mineralisation rates, pH, carbon and N content, and respiration rates of CO₂, N₂O and CH₄ were measured simultaneously. Microbial communities were analysed with qPCR targeting functional genes related to nitrification and denitrification (amoA and nosZ1/2, respectively). Amplicon sequencing of universal prokaryote taxonomic markers and amoA was performed to investigate the response of target and non-target taxa to DMPP addition over time. Statistical analyses are being conducted.