Carlsbergfondet - Disentangling microbial sources of nitrous oxide through dual isotope tracing and multicollector isotope ratio mass spectrometry

Nitrous oxide (N2O) is a strong greenhouse gas and stratospheric ozone scavenger, and its production in the environment is mainly associated with microbial nitrogen transformations. Multiple biochemical pathways can generate N2O but we lack a general understanding of which pathways dominate in different environments and how they are regulated. With the aim of establishing a general mechanistic theory for the microbial production of nitrous oxide, I here apply for funding for a unique, custom-configured isotope ratio mass spectrometer system capable of simultaneous measurement of ten atomic masses including isotopologues of N2O and its fragmentation products N2 and NO. Using N-15 and O-18 as tracers in a newly developed dual isotope labelling approach, the system will be employed to explore the factors that regulate N2O production in oxygen-depleted waters that are hotspots of natural N2O emissions, and in wastewater treatment plants where large contributions of N2O to the carbon footprint are a current concern.