Simulated Nitrogen Deposition Reduces CH4 Uptake and Increases N2O Emission from a Subtropical Plantation Forest Soil in Southern China

To date, few studies are conducted to quantify the effects of reduced ammonium (NH 4 + ) and oxidized nitrate (NO 3 − ) on soil CH 4 uptake and N 2 O emission in the subtropical forests. In this study, NH 4 Cl and NaNO 3 fertilizers were applied at three rates: 0, 40 and 120 kg N ha −1 yr −1 . Soil CH 4 and N 2 O fluxes were determined twice a week using the static chamber technique and gas chromatography. Soil temperature and moisture were simultaneously measured. Soil dissolved N concentration in 0–20 cm depth was measured weekly to examine the regulation to soil CH 4 and N 2 O fluxes. Our results showed that one year of N addition did not affect soil temperature, soil moisture, soil total dissolved N (TDN) and NH 4 + -N concentrations, but high levels of applied NH 4 Cl and NaNO 3 fertilizers significantly increased soil NO 3 − -N concentration by 124% and 157%, respectively. Nitrogen addition tended to inhibit soil CH 4 uptake, but significantly promoted soil N 2 O emission by 403% to 762%. Furthermore, NH 4 + -N fertilizer application had a stronger inhibition to soil CH 4 uptake and a stronger promotion to soil N 2 O emission than NO 3 − -N application. Also, both soil CH 4 and N 2 O fluxes were driven by soil temperature and moisture, but soil inorganic N availability was a key integrator of soil CH 4 uptake and N 2 O emission. These results suggest that the subtropical plantation soil sensitively responses to atmospheric N deposition, and inorganic N rather than organic N is the regulator to soil CH 4 uptake and N 2 O emission.