Long-term organic and inorganic fertilization alters temperature sensitivity of potential N2O emissions and associated microbes

Emissions of the greenhouse gas nitrous oxide (N2O) from soil are sensitive to changes in temperature, nutrient status, pH and other factors. Interactions among these are complex, particularly in agricultural systems where fertilizer-use has interactive influences across many of soil properties. In samples from a long term field trial, temperature sensitivity of N2O emissions, as measured by Q10 values, was higher in soils receiving long-term fertilizer addition. Path analysis was used to predict regulatory mechanisms underlying this and involved integration of soil N status, microbial N-cycling gene quantification and characterization, and measurements of process rates (nitrification, CO2 evolution, and N2O / N2) emissions. Mineralization of soil organic matter and subsequent nitrification was identified as the key process regulating final N2O:N2 molar quotient through the denitrification pathway, with the mechanism associated with soil NH4+ concentration, alteration of pH, and shift in the size and structure of nirS-type denitrifying bacteria. Our results indicate that resource (N-species) coupling between nitrification and denitrificans is affecting rate of denitrification and molar quotient of end product (N2O:N2). As such, interactions between functionally different components of the microbial community have implications for ecosystem function.