Quantifying nitrous oxide emissions from Chinese grasslands with a process-based model

Abstract

As one of the largest land cover types, grassland can potentially play an important role in the ecosystem services of natural resources in China. Nitrous oxide (N₂O) is a major greenhouse gas emitted from grasslands. Current N₂O inventory at a regional or national level in China relies on the emission factor method, which is based on limited measurements. To improve the accuracy of the inventory by capturing the spatial variability of N₂O emissions under the diverse climate, soil and management conditions across China, we adopted an approach by utilizing a process-based biogeochemical model, DeNitrification-DeComposition (DNDC), to quantify N₂O emissions from Chinese grasslands. In the present study, DNDC was tested against datasets of N₂O fluxes measured at eight grassland sites in China with encouraging results. The validated DNDC was then linked to a GIS database holding spatially differentiated information of climate, soil, vegetation and management at county-level for all the grasslands in the country. Daily weather data for 2000–2007 from 670 meteorological stations across the entire domain were employed to serve the simulations. The modelled results on a national scale showed a clear geographic pattern of N₂O emissions. A high-emission strip showed up stretching from northeast to central China, which is consistent with the eastern boundary between the temperate grassland region and the major agricultural regions of China. The grasslands in the western mountain regions, however, emitted much less N₂O. The regionally averaged rates of N₂O emissions were 0.26, 0.14 and 0.38 kg nitrogen (N) ha⁻¹ y⁻¹ for the temperate, montane and tropical/subtropical grasslands, respectively. The annual mean N₂O emission from the total 337 million ha of grasslands in China was 76.5 ± 12.8 Gg N for the simulated years.