Nitrogen deposition increases N2O emission from an N-saturated subtropical forest in southwest China.

Abstract Nitrous oxide (N 2 O) is a major greenhouse gas, with elevated emission being reported from subtropical forests that receive high nitrogen (N) deposition. After 10 years of monthly addition of ammonium nitrate (NH 4 NO 3) or sodium nitrate (NaNO 3) to a Mason pine forest at Tieshanping, near Chongqing city in Southwest China, the simulated N deposition was stopped in October 2014. The results of soil N 2 O emissions monitoring in different seasons during the nitrogen application period showed that nitrogen addition significantly increased soil N 2 O emission. In general, the N 2 O emission fluxes were positively correlated to nitrate (NO 3 ⁻) concentrations in soil solution, supporting the important role of denitrification in N 2 O production, which was also modified by environmental factors such as soil temperature and moisture. After stopping the application of nitrogen, the soil N 2 O emissions from the treatment plots were no longer significantly higher than those from the reference plots, implying that a decrease in nitrogen deposition in the future would cause a decrease in N 2 O emission. Although the major forms of N deposition, NH 4 ⁺ and NO 3 ⁻, had not shown significantly different effects on soil N 2 O emission, the reduction in NH 4 ⁺ deposition may decrease the NO 3 ⁻ concentrations in soil solution faster than the reduction in NO 3 ⁻ deposition, and thus be more effective in reducing N 2 O emission from N-saturated forest soil in the future. Graphical abstract Image 1 Highlights • Effects of increasing/decreasing N deposition on soil N 2 O emission were studied. • N deposition increases soil N 2 O emission from an N-saturated subtropical forest. • Soil N 2 O emissions were positively correlated to NO 3 ⁻ concentrations in soil water. Soil nitrate availability, other than soil temperature and moisture, is key factor determining soil N 2 O emission from an N-saturated subtropical forests. [ABSTRACT FROM AUTHOR]