Development of a Process-Based N2O Emission Model for Natural Forest and Grassland Ecosystems

Forests and grasslands play a significant role in global nitrous oxide (N2O) emission, while a sophisticated model is missing to interpret the microbial processes involved in N2O production and consumption in these ecosystems. A new N2O emission model, MicN model, was developed for natural forest and grassland ecosystems by integrating with Integrated BIosphere Simulator (IBIS). This new model includes four major N2O correlated processes: autotrophic nitrification, heterotrophic nitrification, nitrifier denitrification and denitrifier denitrification. Thirty-nine observation sites, including various forest and grassland ecosystem types, were selected to calibrate and validate IBIS-MicN model. The IBIS-MicN model explained 89% and 85% of observed daily variability in N2O emission for all calibration and validation sites, respectively. In addition, the model successfully predicted the concentrations of two important intermediates (i.e., ammonium and nitrate) for N2O production at nine validation sites. Compared with Forest-DNDC model, IBIS-MicN model performed better in simulating N2O emission, soil NH4+ and NO(3)(-)concentrations. At site scale, the simulated N2O emissions by IBIS-MicN model positively correlated with annual mean soil temperature and annual precipitation, but negatively correlated with soil pH. This study provides an alternative model to estimate global N2O emission from natural forest and grassland ecosystems and to investigate corresponding environmental regulations.