The purpose of this study is to explore the potential changes in the relationship between dynamic light and photosynthesis in high CO₂ environment, so as to provide scientific support for coping with global changes. We characterized dynamic light environment at two heights within rice canopy and dynamic photosynthetic response of leaves at each height (about 45 cm or 90 cm high from the soil of paddy field) in an open canopy and within an open top chamber (OTC) with a high CO₂ of 600 μmol/mol air. The result showed that the averaged photosynthetic photon flux density incident at 90 cm height above the paddy field was 3–4 times higher than that at 45 cm height, but the coefficient of temporal variation in light received at 90 cm height was 55%–60% smaller than that of the lower layer. Flag leaves at 90 cm height showed higher saturated photosynthetic rate and more postillumination CO₂ fixation, while leaves at 45 cm height showed higher photosynthetic rate under low light. In the high CO₂ OTC, light attenuation percentage in canopy tended to increase, compared with leaves outside the OTC; the difference between assimilation rates at the two heights also increased within the OTC. These results suggested that not only the steady-state photosynthetic rate, but also the dynamic photosynthesis in rice leaves may have altered in different ways at different canopy heights, which is to be further influenced by CO₂ environment. 

在当前CO₂环境以及600 μmol/mol air的开顶箱中, 测量水稻冠层离水田泥土45 cm和90 cm处光合有效辐射的变动以及叶片的动态光合速率, 探讨高CO₂环境下光强变动与光合作用关系的潜在变化。结果表明: 1) 水稻冠层90 cm处的平均光强是45 cm处的3~4倍, 但晴天光强的时间变异系数比45 cm处低55%~60%; 2) 上部叶片有更高的饱和光合速率以及照后CO₂固定, 下部叶片有较高的低光光合速率; 3) 高CO₂开顶箱冠层内部的光衰减百分比倾向于增大, 上, 下叶片的光合能力差异增大。因此, 冠层不同高度的光环境可能同时影响叶片的稳定态和动态光合特性, 高CO₂可能加大由不同冠层光环境差异造成的光合特性差异。