西双版纳地区稻田CO2排放通量

采用静态暗箱-气相色谱法对云南西双版纳地区单季稻田CO2排放及氮肥、水热因子对CO2排放的影响进行田间原位观测研究.试验设3个氮肥水平处理:N0(0 kg N hm-2)、N150(150 kg N hm-2)和N300(300 kg N hm-2).结果表明,受一天温度变化的影响,西双版纳地区稻田生态系统呼吸日变化为单峰型,其最大值出现在11:00～13:00之间,最小值出现在凌晨.稻田土壤呼吸呈明显的季节变化趋势,土壤呼吸平均速率为水稻收获后休闲季节>种植前休闲季节>水稻生长季节,差异达到1%显著水平.不同季节影响土壤呼吸的环境因子不同.土壤水分含量低于34%时,土壤呼吸速率与土壤含水量呈正相关,达5%显著水平;地面淹水时,土壤呼吸速率与淹水深度呈1%极显著负相关;水分含量高于38%时,土壤呼吸速率与温度呈极显著指数相关.长期考虑(整个生长季节),氮肥的施用对稻田土壤呼吸和生态系统呼吸无影响;N300处理抑制植株呼吸作用,单位生物量呼吸速率下降.氮肥的施用对土壤呼吸有短期影响,氮肥用量增加,土壤呼吸速率增加.计算得出N0、N150和N300处理年土壤呼吸量分别为6.27、6.31 t C hm-2 a-1和5.89 t C hm-2 a-1;年净固定大气中CO2-C分别为1.41、2.22 t C hm-2 a-1和1 11 t C hm-2 a-1,表明西双版纳稻田生态系统是碳汇.

CO2 emission from paddy soils in Xishuangbanna, Southwest China

Although Xishuangbanna is within the tropics, it has large seasonal climatic variations. Paddy soil has substantial effects on carbon cycle. The CO2 exchange between paddy soil and atmosphere, and the factors influencing this exchange have both become important issues for global carbon\|cycle research. Using the static opaque chamber and gas chromatography technique, CO2 emission from paddy soil and its affecting factors were investigated in Xishuangbanna, SW China. In this study, soils with and without rice plants at three nitrogen fertilization levels (N0, N150 and N300) were examined. We found that diurnal variation of ecosystem respiration could be modeled with single peak curve throughout the rice\|growing season. The maximum and minimum emission rates occurred between 11:00 ~13:00 and at 0:00, respectively. There was a significant correlation between CO2 emission rates and air temperature. Different nitrogen fertilizer levels had the same pattern of ecosystem or soil respiration. Soil respiration varied seasonally, significant at the 1% level. The maximum value occurred during fallow season post\|harvest stage, minimum in the growing season and intermediate in the fallow season before rice transplanting. Soil moisture and temperature were the dominant factors influencing soil respiration. When the soil moisture was below 34%, there was positive linear relationship between soil moisture and soil respiration rate. When soil moisture exceeded 38%, there was an exponential relationship between soil respiration and temperature significant at the 1% level. Throughout the growing season, soil or ecosystem respiration rates under different nitrogen fertilizer levels did not differ, except that the N300 treatment reduced plant respiration. In the short term, nitrogen level increased soil respiration rates. The annual estimated soil respiration was 6.27 t C hm-2,6.31 t C hm-2 and 5.89 t C hm-2 for the N0, N150 and N300 treatments, and the annual net fixation CO2\|C from the atmosphere was 1.41 t C hm-2,2.22 t C hm-2 and 1.11 t C hm-2. Therefore paddy soil in Xishuangbanna serves as a carbon sink at all fertilizer levels.