Impacts of Nitrogen Addition on Nitrous Oxide Emission: Model-Data Comparison

Abstract. The contributions of long-lived nitrous oxide (N₂O) to the global climate and environment have received increasing attention. Especially, atmospheric nitrogen (N) deposition has substantially increased in recent decades due to extensive use of fossil fuels in industry, which strongly stimulates the N₂O emissions of the terrestrial ecosystem. Several models have been developed to simulate N₂O emission, but there are still large differences in their N₂O emission simulations and responses to atmospheric deposition over global or regional scales. Using observations from N addition experiments in a subtropical forest, this study compared six widely-used N₂O models (i.e. DayCENT, DLEM, DNDC, DyN, NOE, and NGAS) to investigate their performances for reproducing N₂O emission, and especially the impacts of two types of N additions (i.e. ammonium and nitrate: NH₄⁺ and NO₃⁻, respectively) and two levels (low and high) on N₂O emission. In general, the six models reproduced the seasonal variations of N₂O emission, but failed to reproduce relatively larger N₂O emissions due to NH₄⁺ compared to NO₃⁻ additions. Few models indicated larger N₂O emission under high N addition levels for both NH₄⁺ and NO₃⁻. Moreover, there were substantial model differences for simulating the ratios of N₂O emission from nitrification and denitrification processes due to disagreements in model structures and algorithms. This analysis highlights the need to improve representation of N₂O production and diffusion, and the control of soil water-filled pore space on these processes in order to simulate the impacts of N deposition on N₂O emission.