| The global climate change is becoming a special concern, which leads to the hot discussion of greenhouse gases emission. So far the data about CH4, CO2 and N2O emission are already available in all the five major rice culture regions in China, but there is still no relevant observation in tropical regions of China. By using static opaque chamber and gas chromatography techniques, field experiments were carried out to investigate CH4, CO2 and N2O fluxes from paddy field in Xishuangbanna, Yunnan, Southwest China. The experiment period lasted from January to December in 2005, including the rice growing season and the fallow stage. Three treatments were applied as the control(NN, no nitrogen fertilizer application), low nitrogen fertilizer level (LN, 150 kg N hm-2) and high nitrogen fertilizer level (HN, 300 kg N hm-2). The results were as follows:1) During rice growing season obvious seasonal changes occurred in CH4 and CO2 fluxes. Greatly controlled by water level and fertilization, N2O fluxes showed no marked seasonal variations.2) There were obvious diurnal variations in CH4 and CO2 fluxes. Three types of diurnal variation of CH4 emission were observed, which were afternoon-maximum mode, two-peak mode with maxima occurred both in the afternoon and at night and the irregular mode. The diurnal changes of CO2 fluxes followed afternoon-maximum pattern, while the diurnal changes of N2O fluxes showed no clear regularity.3) Compared with NN treatment, fertilization had no significant effect on CH4 emission, but remarkably promoted CO2 and N2O emissions in rice growing season. The changes of CH4, CO2 and N2O fluxes could not be fully explained by temperature variations. No pronounced correlations were found between water depth and the fluxes of CH4, CO2 and N2O.4) In rice growing season, the calculated seasonal mean CH4 fluxes were 6.69±0.37, 7.19±0.43 and 6.04±0.31 mg m-2 h-1 for treatments NN, LN and HN, respectively, and the corresponding seasonal mean CO2 fluxes were 543.28±27.57, 680.92±32.26 and 724.58±32.40 mg m-2 h-1, respectively, and accordingly the seasonal mean N2O fluxes were 0.04±0.01, 0.17±0.03 and 0.15±0.03 mg m-2 h-1, respectively.5) The paddy feild emitted CH4, CO2 and N2O in fallow season, however, which demonstrated no clear seasonal changes. Nitrogen fertilizer applied to the field in rice growing period showed little effect on the fallow season emissions of CH4, CO2 and N2O. CH4 and N2O fluxes significantly depended on soil moisture, and CO2 fluxes exponentially increased both with the increase of soil moisture and inner chamber temperature.6) During fallow period, the seasonal average CH4 fluxes were 0.51±0.16, 0.19±0.03 and 0.09±0.02 mg m-2 h-1 for treatments NN, LN and HN, respectively,and the seasonal average CO2 fluxes were 220.56±7.76, 195.18±6.99 and 228.36±7.94mg m-2 h-1, respectively, and the seasonal average N2O fluxes were 0.04±0.00, 0.03±0.01 and 0.04±0.01 mg m-2 h-1, respectively.7) The cumulative CH4, CO2 and N2O emissions from paddy field over rice growing season accounted for 83.26-96.37%,48.24-56.90% and 32.24-71.07% of the annual cumulative CH4, CO2 and N2O emissions, separately, which indicated that the CH4 emissions played a vital role in rice growing season and the CO2 and N2O emissions over fallow season could not be neglected.
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