农田生态系统作为陆地生态系统的重要组成部分，研究其CO2通量和水汽通量的变化特征对于探讨整个陆地生态系统的碳、水循环具有重要的意义。笔者采用涡度相关系统测定了晴天条件下夏玉米农田生态系统抽穗期的水碳通量，分析其日变化特征。研究结果表明：（1）农田生态系统CO2通量随着光合有效辐射的增强而增大，用米氏方程拟合达到极显著水平，最大潜在碳通量为3.63398 mg/(m2· s)；（2）CO2通量上午和下午没有明显的差异，不存在气孔抑制现象；（3）水汽通量随着光合有效辐射的增强而增大，但下午的水汽通量显著大于上午，其原因在于下午的饱和水汽压差远远大于上午，造成下午的蒸腾和蒸发更大；（4）冠层导度随时间的推移基本呈减小的趋势，到11:00 左右基本保持恒定，到14:00左右随着光合有效辐射越来越弱，冠层导度逐渐减小，造成这一结果的原因可能是露水蒸发引起上午冠层导度被高估。
Abstract
Field ecosystem is an important part of terrestrial ecosystem, a study on H2O and CO2 flux change characteristics has significance to exploring carbon and water cycle in the whole terrestrial ecosystem. The corn farmland H2O and CO2 flux was measured under sunshine condition in heading period by the method of eddy covariance system, and the diurnal change characteristics were analyzed. The results showed that: (1) CO2 flux in farmland ecosystem increased with the increase ofphotosynthetically active radiation and the Michaelis-Menten function simulation reached extremely significant level, and the largest potential carbon flux was 3.63398 mg/(m2 · s); (2) CO2 flux had no obvious difference between morning and afternoon, and stomatal inhibition was not existent; (3) water vapor flux increased with the increase of photosynthetically active radiation, but water vapor flux in the afternoon was significantly higher than that in the morning, saturation vapor pressure of the afternoon was much higher than that of the morning, which caused much stronger transpiration and evaporation in the afternoon; (4) canopy conductance showed a reducing trend with time increase, which could reach a balance at 11:00, and reduced gradually at 14:00 with the decrease of photosynthetically active radiation, the reason could be the overestimate of canopy conductance in the morning caused by the evaporation of dew.
关键词
玉米农田；水汽通量；CO2通量；冠层导度；日变化
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Key words
corn farmland; water vapor flux; CO2 flux; canopy conductance; diurnal variation
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