Human activities, such as combustion of fossil fuel, production and utilization of chemical fertilizers, intensification of livestock husbandry, etc. have caused atmospheric nitrogen depositionon the globe to increaseby 3 times, which significantly alters nitrogen recycling in forest ecosystems. Subtropical plantations in China are located in the center of the region very high in atmospheric nitrogen deposition on the globe, where the soils, relatively enriched with nitrogen, are very sensitive to input of extraneous nitrogen, in production and emission of soil nitrous oxide (N₂O). However, in the past, the experiments to simulate N deposition used to have only one type of N fertilizer such as NH₄ NO₃ or urea as N source, without taking into account the difference in in-situ effect between oxidized N and reduced N. In this study, a plantation of pinus elliottii at the Qianyanzhou Subtropical Experiment Station, Chinese Academy of Sciences, was selected as an object in an experiment on controlled N addition. This experiment was designed to have two forms of N fertilizers (NH₄Cl and NaN₃O) and three N application rates (0, 40 and 120 kg hm^-2 a^-1) and laid out in plot randomly. Soil-atmospheric N₂O exchanging fluxes, were measured eight times per month using the static chamber-gas chromatography method, and simultaneously, soil temperature and moisture at 0～10 cm depth, dissolved N concentrations (NO₃^--N, NH₄⁺-N, total dissolved N (TDN), and dissolved organic N (DON)) at 0～15 cm depth were determined for analysis of how the N₂O exchanging flux responded to input of extraneous N and its main affecting factors. Results show that N addition did not affect soil temperature and soil moisture in the subtropical plantation, but did increase significantly soil NO₃^--N, NH₄⁺-N and TDN contents, except for soil DON content, of which the potential mechanisms included preferential absorption of NH₄⁺-N by plants, fixation of NH₄⁺-N by soil organic matter/ minerals, and assimilation of inorganic by plants and soil microbes. Also, N addition significantly promoted soil N₂O emission in the subtropical plantation or by 378%~ 847%; and the effect was higher in plots applied with NH₄Cl than in plots applied with Na NO₃. Moreover, soil N₂O flux was found to be positively and significantly related to soil temperature and soil moisture at 0-10cm depth, which indicates that the hydrothermal factors propelled soil N₂O emission in the subtropical plantation. Also, the change in soil N₂O flux (Δsoil N₂O fluxes, the difference between N treatment and control) was significantly and positively related to that in soil NH₄⁺-N and NO₃^--N contents (Δsoil inorganic N contents), and the relationships could well be fitted with linear and exponential growth equations, respectively. The findings of the study indicate that the increase in soilN₂O content in N-enriched soils is mainly attributed to changes in substrates for nitrifier and denitrifier communities, and hint that soil N₂O emission in the subtropical plantations, South China, is very sesitive to input of extraneous N, and more to reduced NH₄⁺ than to oxidized NO₃^-. The sensitivity is higher than the mean of the globe. Therefore, it is advisable to address reduced NH₄⁺ and oxidized NO₃ separately, in assessing influence of atmospheric N deposition on carbon and N recycling and C budget in future studies. Unfortunately, the failure of this study to determine activities of soil nitrifier and denitrifier communities made it hard to assess relative contributions of various processes, separately, to soil N₂O flux. For future studies, it is recommended to apply ¹⁵N tracer and molecular microbiology in in-depth analysis of the relationships between soil N transformation processes and soil N₂O flux, and coupling effects of key microbial functional groups and soil N transformation and emission processes.