Department of Biology, University of Essex, CO4 3SQ, Wivenhoe Park, Colchester, UK.
Planta. 1991 Sep;185(2):279-86. doi: 10.1007/BF00194071.
The maximum quantum yield of CO2 uptake (Φ), as a measure of light-limited photosynthetic efficiency, of a Brassica napus crop was measured on most days from mid-October until mid-April. During the winter, Φ was decreased by up to 50%. From January to March, leaves exposed to direct sunlight on days with minimum air temperatures near or below 0° C showed significant reductions in Φ. However, control leaves, artificially shaded from direct sunlight on these days, did not show any decrease. This provides statistical evidence for a light-dependent inhibition of CO2 uptake in the field, termed here photoinhibition. Recovery of Φ during warmer interludes was slow, requiring approx. 2-3 d. Concurrent measurements of light interception by the crop canopy and dry-matter accumulation showed that the efficiency with which intercepted light was converted into dry matter varied, declin between January and March to 33% of the value recorded in the warmer autumn months. Conversion efficiency was significantly and positively correlated with quantum yield. In a closed crop canopy during winter, light will be limiting for photosynthesis for much of the time. Under these conditions depression of Φ at the leaf level may contribute significantly to decreased dry-matter accumulation at the crop level, since the light-limited rate of CO2 uptake is likely to govern canopy photosynthetic rate.
利用 CO2 最大量子产量（Φ）来衡量光限制下的光合作用效率，对 10 月中旬至 4 月中旬的大部分时间里油菜作物的最大量子产量进行了测量。在冬季，Φ 降低了多达 50%。从 1 月到 3 月，在最低空气温度接近或低于 0°C 的晴天，直接暴露在阳光下的叶片Φ显著降低。然而，在这些日子里，人工遮挡直接阳光的对照叶片没有显示出任何下降。这为田间光依赖性 CO2 吸收抑制提供了统计证据，这里称为光抑制。在温暖的间歇期，Φ 的恢复速度较慢，需要大约 2-3 天。对作物冠层的光截获和干物质积累的同时测量表明，截获光转化为干物质的效率在 1 月至 3 月之间下降到了温暖秋季月份记录值的 33%。转化率与量子产量呈显著正相关。在冬季封闭的作物冠层中，大部分时间内光合作用都会受到光的限制。在这些条件下，叶片水平上 Φ 的降低可能会导致作物水平上干物质积累的减少，因为 CO2 吸收的光限制速率可能会控制冠层光合作用速率。
