Do increasingly depleted δ15N values of atmospheric N2O indicate a decline in soil N2O reduction?

Growing concentrations of N2O within the atmosphere have been accompanied by decreasing delta N-15 values, provoking the hypothesis of a global decline in the rate of N2O reduction relative to its production in soil. We estimate that the ratio of N2O produced to N2O reduced within the soil profile has declined by about 10-25% relative to its pre-industrial value. To a smaller extent, a reduction in the uptake of atmospheric N2O at the soil surface relative to its emission could also have contributed to the reported isotopic signal. This calls for a greater consideration of the process of N2O reduction in soil and its role in the global turnover of N2O.