Nitrous Oxide Emissions from a Masson Pine Forest Soil in Subtropical Central China

The forest ecosystem plays a pivotal role in contributing greenhouse gases to the atmosphere. In order to characterize the temporal pattern of nitrous oxide (N2O) emissions and identify the key factors affecting N2O emissions from a Masson pine forest in a hilly red-soil region in subtropical central China, we measured the N2O emissions in Jinjing of Hunan Province using the static chamber-gas chromatographic method for 3 years (2010-2012) and analyzed the relationships between the N2O fluxes and the environmental variables. Our results revealed that the N2O fluxes over the 3 years varied from -36.0 to 296.7 mu g N m(-2) h(-1), averaging 18.4 +/- 5.6 mu g N m(-2) h(-1) (n = 3). The average annual N2O emissions were estimated to be 1.6 +/- 0.3 kg N ha(-1) year(-1). The N2O fluxes exhibited clear intra-annual (seasonal) variations as they were higher in summers and lower in winters. Compared with other forest observations in the subtropics, N2O emissions at our site were relatively high, possibly due to the high local dry/wet N deposition, and were mostly sensitive to variations in precipitation and soil ammonium N content. In this work, a multiple linear regression model was developed to determine the influence of environmental factors on N2O emissions, in which a category predictor of "Season" was intentionally used to account for the seasonal variation of the N2O fluxes. Such a model explained almost 40% of the total variation in daily N2O emissions from the Masson pine forest soil studied (P < 0.001).