冬季淹水稻田CH4排放通量及其δ13C的时间变化特征

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-2h-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-2h-1和CH429.8 mg m-2h-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CH43.3 g m-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)。

TEMPORAL VARIATION OF CH4 FLUX AND ITS δ13C FROM WINTER FLOODED RICE FIELD

Investigations were carried out of CH4 emission and its δ13C 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-2 h-1,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,δ13CH4(emitted)increased gradually from-51‰ to-44‰,and then dropped back to-56‰ in the late fallow season.After rice transplanting,δ13C value decreased from-62‰ to-68‰ firstly and then increased swiftly to-60‰,which afterwards remained unchanged for a relatively long time.Late in the season,emitted CH4 became 13C enriched again.The impact of the final drainage on δ13CH4(emitted) was remarkable.The δ13C 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 δ13C value(p<0.05) as well.