Simulated NH4~+-N Deposition Inhibits CH4 Uptake and Promotes N2O Emission in the Meadow Steppe of Inner Mongolia, China

Few studies are conducted to quantify the effects of enhanced N deposition on soil nitrous oxide(N2O) emission and methane(CH4) uptake in the meadow steppe of Inner Mongolia, China. A two-year field experiment was conducted to assess the effects of nitrogen(N) deposition rates(0, 10, and 20 kg N ha-1year-1as(NH4)2SO4) on soil N2O and CH4fluxes. The seasonal and diurnal variations of soil N2O and CH4fluxes were determined using the static chamber-gas chromatography method during the two growing seasons of 2008 and 2009. Soil temperature, moisture and mineral N(NH4~+-N and NO-3-N) concentration were simultaneously measured. Results showed that low level of(NH4)2SO4(10 kg N ha-1year-1) did not significantly affect soil CH4and N2O fluxes and other variables. High level of(NH4)2SO4(20 kg N ha-1year) significantly increased soil NO-3-N concentration by 24.1% to35.6%, decreased soil CH4uptake by an average of 20.1%, and significantly promoted soil N2O emission by an average of 98.2%.Soil N2O emission responded more strongly to the added N compared to CH4uptake. However, soil CH4fluxes were mainly driven by soil moisture, followed by soil NO-3-N concentration. Soil N2O fluxes were mainly driven by soil temperature, followed by soil moisture. Soil inorganic N availability was a key integrator of soil CH4uptake and N2O emission. These results suggest that the changes of availability of inorganic N induced by the increased N deposition in soil may affect the CH4and N2O fluxes in the cold semi-arid meadow steppe over the short term.