稻田CH4的传输

通过对稻田CH_4排放、土壤CH_4产生率以及植物体CH_4传输、气泡、液相扩散这三种排放路径的同时测量后发现:CH_4氧化作用在下午CH_4排放路径通畅时较小;阴雨天气造成CH_4排放率降低会增加CH_4在土壤中的氧化量。早稻CH_4传输效率在6月上、中旬较高,晚稻则在水稻生长初期的7月下旬最高,这主要是两季水稻的生长季节中气候因子的差异造成的。只有在较短的时间尺度内,当水稻植物体、气候因素维持相对恒定时,CH_4产生率和稻田甲烷排放才显出正相关性。 水稻植物体内有明显的CH_4浓度梯度。水稻的切割控制实验发现,通过植物体排放CH_4的比例随季节而变化,在进行单株植物体排放测量时发现了同样结果,早稻和晚稻CH_4通过水稻植物体的传输平均分别占CH_4总体排放的73.18％(43.07—97.88％〕及54.98％(11—99.95％);植物体对CH_4排放的作用在早稻大于晚稻;水稻植物体排放CH_4的能力的季节变化对早、晚稻类似,随着水稻的生长而不断增强,到水稻抽穗中期达到最大,以后则随水稻的成熟而变小;水稻植物体排放CH_4的能力与水稻植物体的高度存在极大的线性正相关。土壤中CH_4的浓度远远大于大气中的CH_4含量(10—10~4倍),根部区域土壤CH_4浓度小于水稻行间土壤中的;在垂直方向,CH_4浓度在14cm深的土壤中最大,与土壤浅层有

THE TRANSPORT OF METHANE IN THE RICE PADDY FIELDS

Simultaneous measurements of CH₄ emission,CH₄ production and transport through rice plant,gas bubble and diffusion in flooded water show that:low oxidation occurs in the afternoon when CH₄ transport efficiency appears higher. CH₄ emission rate is lower in cloudy and raining weather when the CH₄ oxidation rate in the paddy soil higher. Higher transport efficiency appears in early and middle June for the early rice,while for the late rice,it is in late July shortly after rice is transplanted. This difference is mainly caused by different weather trend in the individual rice growing period. Because the relative importance of methane oxidation is not the same in the whole rice growing period,the seasonal variation of CH₄ production rate in the paddy soil can not explain that of CH₄ emission. Better correlation between the two parameters may happen only in a short time period when rice growing status and weather condition remain relatively stable.Obvious concentration gradient is observed in the internal space of rice plant. Higher CH₄ emission rates have been measured in the weeds-growing field than in unplanted field , and the former is very similar to that of rice-planted field. The seasonal variation in non-rice-planted field is different from that in rice planted field,with no peak before harvesting. Experiments show that the portion emitted through rice plant is changing during the growing season. For early and late rice,methane emitted through rice plant accounts in average for 73. 18% (43. 07-97. 88%) and 54. 98% (11. 00 - 99. 95%) of the total flux re- spectively. The above result shows that the role of rice plant in methane emission is greater for early rice. The seasonal variation of transport ability of rice plant appears similar for early and late rice, which increases with the time and reaches maximum at mid-heading stage,then decreases with rice riping. The CH₄ transport ability of rice correlates well linearly with the plant height. CH₄ concentration in soil pore water is much higher than that in the atmosphere(10 -10⁴ times). Less amount of methane desolved in root soil has been found than that in the soil between rice-plants. Maximum concentration of CH₄ appears at the depth of 14cm,appearent concentra tion gradient is observed along verticeal direction. Very good correlation between CH₄ emission and the amount desolved in root soil has been observed.The CH₄ emitted by gas bubble accounts in average for 24. 14% and 40. 52% of the total flux respectively for early and late rice. At the beginning of late rice planting, the aboundance of organic matter in the soil and hot weather condition make the ebulltion flux very high. The CH₄ bubble emission is higher in the unplanted field than that in rice-planted one. The concentration gradient to the water surface in flooded water can be easily seen, which accounts for 2. 68 % and 4. 50% of total flux for early and late rice respectively.