“双季稻-冬闲田”生态系统碳交换动态变化及其影响因素

Seasonal variation in carbon exchange and its modulating factors of a double cropping rice ecosystem in Southern China

采用涡度相关技术对南方"双季稻-冬闲田"生态系统CO_2通量进行了一年的连续监测,分析了"双季稻-冬闲田"生态系统碳交换[净碳交换量(NEE)、总初级生产力(GPP)和生态系统总呼吸(Reco)]的动态变化及其影响因子。结果表明:南方"双季稻-冬闲田"生态系统NEE具有明显的日变化和季节变化,NEE月平均日变化在生长季表现为较明显的"U"型曲线,不同月份"U"型高度不同;NEE季节变化存在明显的两个吸收期(NEE为负)和三个排放期(NEE为正),NEE在早稻和晚稻的生长季有两个明显的碳吸收期,早稻平均值为-0.58 g C·m^(-2)·d^(-1),最大值出现在2015年6月20日,为-1.77 g C·m^(-2)·d^(-1),晚稻平均值为-1.28 g C·m^(-2),最大值出现在2015年9月19日,为-2.23 g C·m^(-2)·d^(-1);冬闲期存在两个碳排放期,平均值为2.68 g C·m^(-2)·d^(-1)。水稻种植期间白天的净碳交换受光合有效辐射的影响显著,夜间的净碳交换受5 cm土壤温度的显著影响,温度低时的冬闲期温度敏感性高于温度高时的双季稻种植期。全年的NEE总和表现为碳排放,达778.4 g C·m^(-2),GPP为1 643.7 g C·m^(-2),Reco为2 425.8 g C·m^(-2)。因此,南方"双季稻-冬闲田"生态系统有可观的固碳减排潜力。

In this study, the CO2 flux of a typical double cropping rice ecosystem was continuously monitored by the eddy covariance technique. The carbon exchange [Net ecosystem exchange（NEE）, Gross primary productivity（GPP） and Ecosystem respiration（Reco）] in the double cropping rice ecosystem and its regulatory factors were analyzed. The results showed that the NEE of the double cropping rice e-cosystem had clear diurnal and seasonal variations. The daily diurnal variation in NEE showed a significant U-shaped curve during the growing season, and the peak values were different for each month. The seasonal variation in NEE showed two uptake periods（when NEE was negative） and three emission periods（when NEE was positive）. The NEE results showed two significant carbon uptake periods in the growing season of the early rice stage and the late rice stage. The average daily value for NEE in early rice was-0.58 g C·m^（-2）, and the maximum appeared on June 20（-1.77 g C·m^（-2））. The average value for NEE in late rice was-1.28 g C·m^（-2） and the maximum appeared on September 19（-2.23 g C·m^（-2））. There were two carbon emission periods during the non-crop growing period in winter, where the mean value was 2.68 g C·m^（-2）. The daytime NEE during rice cultivation was significantly affected by photosynthetically active radiation. The nighttime NEE was significantly affected by the soil temperature at 5 cm depth, and the temperature sensitivity at the winter fallow stage was higher than in the double cropping season when the temperature was higher. The total NEE for the whole year indicated that the double cropping rice ecosystem created carbon emissions that reached 778.4 g C·m^（-2）, while GPP was 1 643.7 g C·m^（-2）, and Recowas 2 425.8 g C·m^（-2）.Therefore, the southern double-cropping rice ecosystem has a very significant potential for carbon sequestration and emission mitigation.