The contrasting effects of deposited NH4+ and NO3- on soil CO2, CH4 and N2O fluxes in a subtropical plantation, southern China

Background and aims: Deposited NH4+ and NO3- 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 NH4+ and NO3- 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 (NH4Cl and NaNO3) 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 CO2, CH4 and N2O 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 N2O emission factor (EF) were calculated. Results: Low level of NaNO3 addition significantly increased cumulative annual soil CO2 emission by 33.7%. N addition significantly promoted annual soil N2O emission by 2.4-6.9 folds; moreover, ammonium-N addition had a greater promotion to soil N2O emission than nitrate-N addition. However, short-term N addition did not change soil CH4 uptake. Also, soil CO2 and N2O fluxes were positively correlated with soil temperature and moisture, while soil CH4 uptake was only driven by soil moisture. Overall, elevated N addition increased the total GWP, and changed the temperature sensitivity (Q(10)) of soil CO2 and N2O 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. (C) 2015 Elsevier B.V. All rights reserved.