Department of Biology, University of Essex, Wivenhoe Park, C04 3SQ, Colchester, Essex, UK.
Photosynth Res. 1994 Dec;42(3):217-25. doi: 10.1007/BF00018264.
Changes in the photosynthetic light-response curve during leaf development were determined for the fourth leaf of maize crops sown on 23 April and 10 June. Temperatures were unusually mild during late spring/early summer and neither crop experienced chilling damage. The concept of thermal time was used to take into account the effects of different temperature regimes on developmental stage, thereby enabling photosynthetic light-response data to be combined for both crops to describe the general response. Large variations in the upper asymptote (Asat) and convexity (Θ) of the light-response curve occurred during leaf development, but the maximum quantum yield of CO2 assimilation remained relatively constant throughout. Dark respiration rates showed a small but significant decrease with leaf age and generally ranged between 5 and 10% of Asat. A simple mathematical model was developed to assess the sensitivity of daily leaf photosynthesis (AL) to reductions in the Asat, Θ and the initial slope (Φ) of the light-response curve at different stages of leaf development. On bright sunny days, and at all developmental stages, AL was ca. twice as sensitive to reductions in Asat than to reductions in Φ and Θ. In overcast conditions, however, all three parameters contributed significantly to reductions in leaf photosynthesis, although the contribution of Φ was greatest during early leaf growth, while older leaves were most sensitive to depressions in Asat. The implications of these results for modelling the sensitivity of canopy photosynthesis to chill-induced photoinhibition of the light-response curve are discussed.
对 4 月 23 日和 6 月 10 日播种的玉米作物第四片叶子的光合作用光响应曲线在发育过程中的变化进行了测定。春末/初夏期间的温度异常温和，两种作物都没有受到冷害。利用热时间的概念来考虑不同温度条件对发育阶段的影响，从而可以合并两种作物的光合作用光响应数据来描述一般响应。在叶片发育过程中，光响应曲线的上渐近线（Asat）和凸度（Θ）发生了很大变化，但 CO2 同化的最大量子产量在整个过程中相对保持不变。暗呼吸速率随叶片年龄略有下降，但具有显著意义，通常在 Asat 的 5%至 10%之间。开发了一个简单的数学模型，以评估在叶片发育的不同阶段，Asat、Θ 和光响应曲线初始斜率（Φ）降低对每日叶片光合作用（AL）的敏感性。在阳光明媚的日子里，以及在所有发育阶段，AL 对 Asat 降低的敏感性比对 Φ 和 Θ 降低的敏感性高约两倍。然而，在阴天条件下，所有三个参数都对叶片光合作用的降低有显著贡献，尽管在早期叶片生长过程中 Φ 的贡献最大，而较老的叶片对 Asat 的降低最为敏感。讨论了这些结果对模型化冠层光合作用对光响应曲线冷诱导光抑制的敏感性的影响。
