Modeling of N2O emission from unmanaged terrestrial ecosystem soils

Nitrous oxide (N2O) is not only an important greenhouse gas, but also impacts stratospheric ozone. Soils under natural vegetation and agriculture are the major sources of N2O through nitrification and denitrification processes. Current estimates of N2O emissions on regional to global scales are largely based on the upscaling of limited measurements from specific measurement sites. These estimates have large uncertainties because of the heterogeneity of soils and the seasonal and inter－annual variability in the processes that control the nitrification and denitrification of soils. In this study, I employ a land surface model, the Integrated Science Assessment Model (ISAM), to model the global N2O emissions from terrestrial ecosystem soils. The model is calibrated and evaluated with field measurements of N2O from different sites with different biome types, climate conditions, and soil properties. The model is able to capture the temporal trends and magnitude of the N2O emissions under different climate and soil moisture conditions. Our results show that warm and moist tropical forest and areas with high nitrogen deposition are the major sources of N2O emissions, while there are significantly low emissions from the high latitude ecosystems as a result of low temperature and high soil nitrogen limitation. These results are consistent with both measurements and previous modeling studies. Global experiments are also conducted to study the effect of different environmental factors on soil N2O emission, such as CO2, climate, land use changes and nitrogen deposition. Land use change is the major effect on global N2O emission. Nitrogen deposition is the second most important factor, and contributes to the increase of N2O emission.The impact of CO2 and climate on N2O emission are very uncertain. The former depends on the competition between plants and microbes, and the latter is controlled by the combined effect of precipitation and temperature