Enhanced nitrous oxide emissions caused by atmospheric nitrogen deposition in agroecosystems over China

Atmospheric nitrogen (N) deposition in China has been the largest worldwide. Yet the impacts of atmospheric N deposition on soil N₂O emissions were often ignored by previous studies. Thus, we investigated how N deposition affected N₂O emissions over China using the process-based model (DNDC, DeNitrification-DeComposition). Total soil N inputs were 194 kg N ha^-1 in agricultural systems over China in 2010, including chemical N fertilizer (78%), atmospheric N deposition (12%), and crop residues N (10%). Annual N₂O emissions induced by N deposition were estimated at 97 Gg N, occupying 43% of total soil N₂O emissions (228 Gg N) in agricultural systems over China. In particular, the largest N₂O emissions caused by atmospheric N deposition were found in South China, followed by North China Plain and Southwest China. The efficiency of N deposition generating N₂O emissions (3.0%) over China was 4 times than that of N fertilizer (0.7%). N₂O emissions induced by N deposition increased from 81 Gg in 2000 to 93 Gg in 2014 (by 1% yr^-1), which was consistent with the long-term trend of N deposition. This suggests N deposition accelerated soil N₂O emissions largely contributing to global warming. Our results also indicated that 62% and 10% of soil N₂O emissions were reduced by applying a nitrification inhibitor and N fertilizer with 20% decrease. We highlight the significance of considering N deposition in determining total soil N₂O emissions over China. The results provide an important scientific basis for the prediction of greenhouse effect caused by N deposition over China.