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Nathaniel E. Ostrom, Dept. of Integrative Biology, Michigan State University
Nitrous oxide (N2O) recently became the third most important greenhouse gas contributing to global climate change and is the most important mechanism of stratospheric ozone destruction. The IPCC recently closed the global budget for N2O but the uncertainty in the source and sink terms is nearly as great as the fluxes. Agriculture is the greatest source of atmospheric N2O yet accurate assessment of fluxes is challenged by great spatial and temporal variability. For example, 90% or more of the annual flux from an agricultural field can occur over a period of a few days and flux measurements taken meters apart can vary by an order of magnitude. In this talk I will explore how the surprising isotopic complexity of N2O can provide insights into the causes of the “hot spot” and “hot moment” behavior of N2O fluxes. I will demonstrate how stable isotope abundances can reveal the microbial pathways of N2O production in agricultural and aquatic environments. The possibility of abiotic N2O production will be explored within the Antarctic Dry Valley’s Lake Vida. At -13 oC Lake Vida contains one of the coldest viable microbial ecosystems on Earth and the highest concentration of N2O reported for an aquatic environment. Lastly, I will present results on recent experiments that demonstrate how changes in soil properties (porosity and water content) and leave litter affect both the flux of at N2O as well as the microbial production pathway at micro-scales in soil. Collectively these studies provide insights into the causes of hot spot and hot moment behavior in N2O fluxes and the promise of a more tightly constrained global N2O budget.