Simulated Nitrogen Deposition Reduces CH(4) Uptake and Increases N(2)O 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.