冬季淹水稻田CH4排放通量及其δ13C的时间变化特征

摘要

通过田间试验研究了持续淹水稻田冬季休闲期和水稻生长期CH4排放通量及其稳定性碳同位组成的时间变化.结果表明:CH4排放在冬季休闲期从4月份呈逐渐上升趋势,至6月份出现排放峰,为CH46.4 mg m-2 h-1；水稻移栽后则迅速增加,于7月和8月出现两个排放峰,分别为CH423.1 mg m-2 h-1和CH429.8 mg m-2 h-1,此后急剧下降,末期稻田排水落干期间出现一个排放峰.冬季休闲期CH4排放总量为CH43.3gm-2,占全年排放总量的8.9％.稻田排放的δ13CH4在冬季休闲期后期逐渐从-51‰上升至- 44‰,然后下降至- 56‰.水稻移栽后,δ13C值从- 62‰迅速降至- 68‰,然后慢慢上升至- 60‰,并在较长一段时间内保持不变,后期再次富集13C.末期排水落干对排放δ13CH4影响显著.排放δ13CH4在水稻生长期较冬季休闲期低得多,原因在于冬季休闲期的CH4氧化率很高(60％～90％),而水稻生长期的CH4氧化率相对较低( 10％ ～ 80％).全观测期内,CH4排放通量的季节变化均与土壤温度显著正相关(p＜0.01),与土壤Eh显著负相关(p＜0.01),与δ13CH4呈显著负相关(p＜0.05).%Investigations were carried out of CH4 emission and its S C values from a rice field under continuous flooding throughout the fallow and following rice seasons. Results show that in the fallow season CH4 flux rose from April and reached a peak value, about 6.4 mg m~2 h"1 , in June. After rice transplanting, CH4 flux increased quickly at the beginning of the rice season and two peaks occurred in July and August, reaching 23. 1 and 29. 8 mg m h , respectively, which was followed by a rapid decrease. Then another peak appeared during the final drainage before rice harvest. The total CH4 emission in the fallow season amounted to 3.3 g m~2, accounting for 8.9% of the annual total emission. On the other hand, 8'3CH4 (emilled) increased gradually from -5%c to -44%e, and then dropped back to - 56%e in the late fallow season. After rice transplanting, 8 C value decreased from - 62%e to -68%e firstly and then increased swiftly to -60%e, which afterwards remained unchanged for a relatively long time. Late in the season, emitted CH4 became C enriched again. The impact of the final drainage on 8 CH4 (eniilled) was remarkable. The 8 C value of emitted CH4 was heavier in the fallow season than in the rice season, because the fraction of CH4 oxidized was higher in the fallow season (60%~90% ) than during the following rice season (10%~80% ). Within the whole observation period, the temporal variation of CH4 flux was positively related to soil temperature (p <0.01) , but negatively related to soil Eh (p <0.01) and to 513C value (/><0.05) as well.