恒定环境条件下西洋参叶片光合作用的日变化

为了探索西洋参叶片光合作用日变化的内在因素，以人工气候葙内培养的西洋参为材料．对1日中叶片光合作用的变化及某些生理生化指标进行了测定。结果表明：在恒定环境条件下西洋参叶片光合作用日变化表现下午低于上午的日变化规律．即呈日下降变化．日下降范围为15％--20％。1日中叶片气孔导度和蒸腾作用也呈下降变化，但气孔导度日下降百分率大于蒸腾作用的日下降率．气孔导度的日下降百分率与光合日下降百分率基本一致。蒸腾作用和水分利用效率的日下降百分率低于光合日下降百分率。胞间CO2浓度下午呈上升变化趋势，说明光合日下降属于非气孔限制作用。西洋参叶片光合速率与比叶重及叶片淀粉含量均呈现出极显著负相关关系，叶片光合产物的积累是发生光合日下降现象的重要原因之一。

Diurnal Changes of Photosynthesis of Panax quinquefolium Leaves under Invariable Environmental Conditions

In order to investigate the effect of the internal factors on the diurnal changes of photosynthesis in Panax quinquefolium, diurnal changes of photosynthesis and some physiological and biochemical characteristics of Panax quinquefolium leaves grown under artificial plant environmental chamber were measured. The results are as follows. Net photosynthetic rate(Pn) in the morning(8:00 - 11 :00) was higher than that in the afternoon(13:00 - 16:00) during a day, and showed daily depression. Daily depression percentage was in the range of 15% - 20% . Stomatal conductance ( gs) and transpiration rate (Tr) also showed daily depression like Pn. Daily depression of gs was higher than that of Tr, and gs showed similar change to that of Pn. Intercellular CO2 concentration ( Ci ) was increased in the afternoon (13:00 -16:00), which indicated that daily depression of Pn was not a stomatal limiting. Specific leaf weight (SLW, dry weight per unit leaf area) and starch content increased from morning to afternoon persistently, and they were significantly in negative relation with Pn . So it can be presumed that accumulation of photosynthetic products is an important internal factor in daily depression of Pn.