Soil GHG fluxes are altered by N deposition: New data indicate lower N stimulation of the N O flux and greater stimulation of the calculated C pools.

The effects of nitrogen (N) deposition on soil organic carbon (C) and greenhouse gas (GHG) emissions in terrestrial ecosystems are the main drivers affecting GHG budgets under global climate change. Although many studies have been conducted on this topic, we still have little understanding of how N deposition affects soil C pools and GHG budgets at the global scale. We synthesized a comprehensive dataset of 275 sites from multiple terrestrial ecosystems around the world and quantified the responses of the global soil C pool and GHG fluxes induced by N enrichment. The results showed that the soil organic C concentration and the soil CO , CH and N O emissions increased by an average of 3.7%, 0.3%, 24.3% and 91.3% under N enrichment, respectively, and that the soil CH uptake decreased by 6.0%. Furthermore, the percentage increase in N O emissions (91.3%) was two times lower than that (215%) reported by Liu and Greaver (Ecology Letters, 2009, 12:1103-1117). There was also greater stimulation of soil C pools (15.70 kg C ha  year per kg N ha  year ) than previously reported under N deposition globally. The global N deposition results showed that croplands were the largest GHG sources (calculated as CO equivalents), followed by wetlands. However, forests and grasslands were two important GHG sinks. Globally, N deposition increased the terrestrial soil C sink by 6.34 Pg CO /year. It also increased net soil GHG emissions by 10.20 Pg CO -Geq (CO equivalents)/year. Therefore, N deposition not only increased the size of the soil C pool but also increased global GHG emissions, as calculated by the global warming potential approach.