鄱阳湖平原直播稻CH_(4)通量及其与CO_(2)通量的综合温室效应

CH_(4)Fluxes and Their Comprehensive Greenhouse Effects with CO_(2)Fluxes in Direct-seeded Rice in Poyang Lake Plain

稻田是一个既排放CH_(4)又吸收CO_(2)的复杂生态系统,在全球水碳循环和碳收支中发挥着重要作用.利用涡度相关法得到2020年鄱阳湖平原双季直播稻田的CH_(4)和CO_(2)通量,定量揭示了稻田碳通量变化特征、累积量和2种温室气体的综合温室效应.结果表明,双季直播稻田为CH_(4)排放源,全生育期排放量为52.6 g·m^(-2),日均排放0.208 g·(m^(2)·d)^(-1).CH_(4)通量具有明显的季节变化特征,强排放期(排放峰)集中在早稻生长中期和晚稻生长前期,早稻85.5%和晚稻92.1%的CH_(4)在强排放期被释放,日尺度峰值分别为0.638 g·(m^(2)·d)^(-1)和1.282 g·(m^(2)·d)^(-1).CH_(4)通量日变化呈显著单峰型、不显著单峰型和无规律型,强排放期主要为单峰型,该型式下早稻季峰值0.453μmol·(m^(2)·s)^(-1)和晚稻季峰值0.977μmol·(m^(2)·s)^(-1)均出现在14:00~15:00,且在12:30~16:00维持较高排放速率.早稻和晚稻全生育期CO_(2)累积量分别为-990.4 g·m^(-2)和-1156.6 g·m^(-2),合计为-2147.0 g·m^(-2).双季稻田CH_(4)排放和CO_(2)交换的综合温室效应(以CO_(2)当量计)为-673.6 g·m^(-2),表现为降温效应.当评价稻田温室效应时若不考虑CH_(4)排放,将低估1473.4 g·m^(-2)的CO_(2)当量排放,占净CO_(2)吸收量的68.6%.

Paddy fields are complex ecosystems that both emit CH_(4)and absorb CO_(2),which plays an important role in the global water-carbon cycle and carbon budget.In this study,the CH_(4)fluxes and CO_(2)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 CH_(4)emission,and the emission during the whole growth period was 52.6 g·m^(-2),with an average daily emission of 0.208 g·(m^(2)·d)^(-1).CH_(4)emission and daily average emission in the early rice season were 20.7 g·m^(-2)and 0.188 g·(m^(2)·d)^(-1),respectively,which were lower than the emissions of 31.9 g·m^(-2)and 0.255 g·(m^(2)·d)^(-1)in the late rice season.CH_(4)flux had significant seasonal variation characteristics.The strong emission period(emission peak)of CH_(4)was concentrated in the middle growth stage of early rice and the early growth stage of late rice.A total of 85.5%of CH_(4)in the early rice season and 92.1%of CH_(4)in the late rice season were released during the strong emission periods,and seasonal peak values were 0.638 g·(m^(2)·d)^(-1)and 1.282 g·(m^(2)·d)^(-1),respectively.The diurnal variation characteristics of CH_(4)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 0.453μmol·(m^(2)·s)^(-1)in the early rice season and 0.977μmol·(m^(2)·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 CO_(2)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 CH_(4)emission and CO_(2)exchange in the double-cropping paddy field was-673.6 g·m^(-2)(calculated using the CO_(2)equivalent),which showed a cooling effect.Excluding CH_(4)emissions when evaluating the greenhouse effect of the paddy field,the CO_(2)equivalent emission of 1473.4 g·m^(-2)would be underestimated,accounting for 68.6%of the net CO_(2)absorption.Considering CH_(4)emissions,CO_(2)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.