稻田是既排放CH4又吸收CO2的复杂生态系统,在全球水碳循环和碳收支中起着重要作用。在这项研究中,利用涡度协方差方法,得到了鄱阳湖平原地区2020年双季直播稻田CH4通量和CO2通量,和变化特征,在整个生长期的积累,定量揭示了两种温室气体的综合温室效应。结果表明,鄱阳湖平原双季直播稻田是CH4排放源,整个生长期的排放量为52.6g·m-2,平均日排放量为0.208g·(m2·d)-1。早稻季节CH4排放量和日平均排放量分别为20.7g·m-2和0.188g·(m2·d)-1,低于晚稻季节31.9g·m-2和0.255g·(m2·d)-1的排放量。CH4通量具有显著的季节变化特征。CH4的强排放期(排放峰)集中在早稻的中间生育期和晚稻的早期生育期。在强排放期,早稻季CH4共释放85.5%,晚稻季CH4释放92.1%,季节峰值分别为0.638g·(m2·d)-1和1.282g·(m2·d)-1。CH4通量的日变化特征表现为三种类型:明显的单峰型,非明显的单峰型,不规则类型。强发射周期主要是单峰型,早稻季0.453μmol·(m2·s)-1和晚稻季0.977μmol·(m2·s)-1的峰值出现在14:00-15:00,并在12:30-16:00保持高排放率。早稻和晚稻整个生育期的CO2累积量分别为-990.4g·m-2和-1156.6g·m-2,总量为-2147.0g·m-2。双季稻田CH4排放和CO2交换的综合温室效应为-673.6g·m-2(以CO2当量计算),显示出冷却效果。在评估稻田的温室效应时,不包括CH4排放,1473.4g·m-2的二氧化碳当量排放量将被低估,占CO2净吸收量的68.6%。考虑到CH4排放,二氧化碳交换,和水稻收获造成的碳排放,鄱阳湖平原两季直播稻田是温室气体排放源。
Paddy fields are complex ecosystems that both emit CH4 and absorb CO2, which plays an important role in the global water-carbon cycle and carbon budget. In this study, the CH4 fluxes and CO2 fluxes of double-cropping direct-seeded rice fields in 2020 in the Poyang Lake Plain were obtained using the eddy covariance method, and the variation characteristics, accumulation in the whole growth period, and comprehensive greenhouse effects of two greenhouse gases were quantitatively revealed. The results showed that, the double-cropping direct-seeded rice field in Poyang Lake Plain was the source of CH4 emission, and the emission during the whole growth period was 52.6 g·m-2, with an average daily emission of 0.208 g·(m2·d)-1. CH4 emission and daily average emission in the early rice season were 20.7 g·m-2 and 0.188 g·(m2·d)-1, respectively, which were lower than the emissions of 31.9 g·m-2 and 0.255 g·(m2·d)-1 in the late rice season. CH4 flux had significant seasonal variation characteristics. The strong emission period (emission peak) of CH4 was concentrated in the middle growth stage of early rice and the early growth stage of late rice. A total of 85.5% of CH4 in the early rice season and 92.1% of CH4 in the late rice season were released during the strong emission periods, and seasonal peak values were 0.638 g·(m2·d)-1 and 1.282 g·(m2·d)-1, respectively. The diurnal variation characteristics of CH4 flux showed three types:obvious unimodal type, non-obvious unimodal type, and irregular type. The strong emission period was mainly the unimodal type, and the peak values of 0.453 μmol·(m2·s)-1 in the early rice season and 0.977 μmol·(m2·s)-1 in the late rice season appeared at 14:00-15:00 and maintained a high emission rate at 12:30-16:00. The CO2 accumulation in the whole growth period of early rice and late rice was -990.4 g·m-2 and -1156.6 g·m-2, respectively, and the total was -2147.0 g·m-2. The comprehensive greenhouse effect of CH4 emission and CO2 exchange in the double-cropping paddy field was -673.6 g·m-2 (calculated using the CO2 equivalent), which showed a cooling effect. Excluding CH4 emissions when evaluating the greenhouse effect of the paddy field, the CO2 equivalent emission of 1473.4 g·m-2 would be underestimated, accounting for 68.6% of the net CO2 absorption. Considering CH4 emissions, CO2 exchanges, and carbon emissions caused by rice harvest, the two-season direct seeding paddy field in Poyang Lake Plain was the source of greenhouse gas emissions.