Fluxes of CH4 and N2O from soil under a tropical seasonal rain forest in Xishuangbanna, Southwest China

CH4 and N2O fluxes from soil under a tropical seasonal rain forest in Xishuangbanna, Southwest China were measured for one year using closed static chamber technique and gas chromatography method. Three treatments were set in the studied field: (A) litter-free, (B) with litter, and (C) with litter and seedling. The results showed that the soil in our study was a sink of atmospheric CH4 and source of atmospheric N2O. The observed mean CH4 fluxes from treatments A, B, and C were -50.0 +/- 4.0, -35.9 +/- 2.8, -31.6 +/- 2.8 mu gC/(m(2).h), respectively, and calculated annual fluxes in 2003 were -4.1, -3.1, and -2.9 kgC/hm(2), respectively. The observed mean N2O fluxes from treatments A, B, and C were 30.9 +/- 3.1, 28.2 +/- 3.5, 50.2 +/- 3.7 mu gN/(m(2).h), respectively, and calculated annual fluxes in 2003 were 2.8, 2.6, and 3.7 kgN/hm(2), respectively. Seasonal variations in CH4 and N2O fluxes were significant among all the three treatments. The presence of litter decreased CH4 uptake during wet season (P < 0.05), but not during dry season. There was a similar increase in seedlings-mediated N2O emissions during wet and dry seasons, indicating that seedlings increased N2O emission in both seasons. A strong positive relationship existed between CH4 fluxes and soil moisture for all the three treatments, and weak relationship between CH4 fluxes and soil temperature for treatment B and treatment C. The N2O fluxes correlated with soil temperature for all the three treatments.