Linking Annual N(2)O Emission in Organic Soils to Mineral Nitrogen Input as Estimated by Heterotrophic Respiration and Soil C/N Ratio

Organic soils are an important source of N(2)O, but global estimates of these fluxes remain uncertain because measurements are sparse. We tested the hypothesis that N(2)O fluxes can be predicted from estimates of mineral nitrogen input, calculated from readily-available measurements of CO(2) flux and soil C/N ratio. From studies of organic soils throughout the world, we compiled a data set of annual CO(2) and N(2)O fluxes which were measured concurrently. The input of soil mineral nitrogen in these studies was estimated from applied fertilizer nitrogen and organic nitrogen mineralization. The latter was calculated by dividing the rate of soil heterotrophic respiration by soil C/N ratio. This index of mineral nitrogen input explained up to 69% of the overall variability of N(2)O fluxes, whereas CO(2) flux or soil C/N ratio alone explained only 49% and 36% of the variability, respectively. Including water table level in the model, along with mineral nitrogen input, further improved the model with the explanatory proportion of variability in N(2)O flux increasing to 75%. Unlike grassland or cropland soils, forest soils were evidently nitrogen-limited, so water table level had no significant effect on N(2)O flux. Our proposed approach, which uses the product of soil-derived CO(2) flux and the inverse of soil C/N ratio as a proxy for nitrogen mineralization, shows promise for estimating regional or global N(2)O fluxes from organic soils, although some further enhancements may be warranted.