Firestone et al. 1980

Firestone MK, Firestone RB, Tiedje JM. 1980. Nitrous oxide from soil denitrification: Factors controlling its biological production. Science 208: 749-751.

These authors measured the faction of N2O in nitrogen gas outputs from soil slurries under a range of conditions of substrate and oxygen availability. Slurries were employed to avoid problems associated with diffusion of materials through a soil matrix, and the process of denitrification was studied using isotopic tracers, especially in the form of 13N in nitrate and other inputs.

The controls on the production of N2O from denitrification are the concentration of nitrite (NO2-) and the availability of oxygen (O2), with time-since-anoxic another important factor. Increasing nitrite increases N2O production and increasing NO3- does as well, but less strongly, suggesting the role of NO3- is indirect, and it is the NO2- produced from NO3- that matters. Aerobic conditions inhibit denitrification, rendering the entire pathway moot. The establishment of anaerobic conditions turns on denitrification, but in a stepwise process apparently related to protein synthesis. In a series of experiments, these authors found that in the initial period of anaerobiosis, N2 is the major output. Later, N2O production increases without an increase in its consumption, and N2O is the major output. Finally, N2O consumption catches up with production, and N2 is once again the major output. Adding O2 increases the proportion of total denitrification output that is N2O, but eventually O2 does inhibit denitrification completely.