The contrasting effects of deposited NH4+ and NO3− on soil CO2, CH4 and N2O fluxes in a subtropical plantation, southern China
Abstract Background and aims Deposited NH 4 + and NO 3 − differently affect soil carbon (C) and nitrogen (N) cycles due to their contrasting actions in terrestrial ecosystems. However, little information on the effects of exogenous NH 4 + and NO 3 − inputs on the exchange of greenhouse gases (GHGs) from the subtropical plantation soils as well as their contribution to global warming is available to date. Methods Based on a field experiment, two-form (NH 4 Cl and NaNO 3 ) and two-level (40 and 120 kg N ha −1  yr −1 ) of N addition, in a slash pine plantation of southern China, we investigated soil CO 2 , CH 4 and N 2 O fluxes and related auxiliary variables (soil temperature and moisture) twice a week using static chamber–gas chromatography. The total global warming potential (GWP) of soil GHG fluxes and N 2 O emission factor (EF) were calculated. Results Low level of NaNO 3 addition significantly increased cumulative annual soil CO 2 emission by 33.7%. N addition significantly promoted annual soil N 2 O emission by 2.4–6.9 folds; moreover, ammonium-N addition had a greater promotion to soil N 2 O emission than nitrate-N addition. However, short-term N addition did not change soil CH 4 uptake. Also, soil CO 2 and N 2 O fluxes were positively correlated with soil temperature and moisture, while soil CH 4 uptake was only driven by soil moisture. Overall, elevated N addition increased the total GWP, and changed the temperature sensitivity (Q 10 ) of soil CO 2 and N 2 O fluxes. Conclusions These results suggest that chronic atmospheric N deposition changes soil-atmospheric GHG fluxes in the subtropical plantation of southern China depending on the levels and forms of N input, and would exacerbate global warming.