北方冬小麦旗叶光饱和点探讨

为准确估算冬小麦旗叶光饱和点的范围，采用Li-6400-40荧光探头提供不同光合有效辐射强度，同步测量了不同品种（系）、不同时期(抽穗期、开花期和灌浆期)、不同CO₂浓度及不同施氮量下小麦旗叶的气体交换和荧光参数。结果表明，运用直角双曲线修正模型拟合的饱和光强与实际观测值较为接近。外界CO₂浓度和施氮量对小麦旗叶光饱和点具有较大影响，低CO₂浓度(300 μmol·mol^-1)和低施氮量(70 kg·hm^-2)下光饱和点均比较低；而品种（系）间和测定时期间小麦旗叶光饱和点整体差异不明显。正常条件下，小麦旗叶的光饱和点整体集中在 1 700~2 000 mol·m^-2·s^-1范围，远高于目前普遍认为的1 200 mol·m^-2·s^-1，这与小麦叶片的阳生特点及实际观测结果相一致。早期广泛采用的老版本光合助手(Photosynthesis Assistant)的拟合结果明显低于观测值(P<0.05)。综合试验结果推测，早期光饱和点的研究结果偏低可能与测量CO₂浓度、氮素营养以及所用的拟合模型等因素有关。

Study on the Light Saturated Point of Winter Wheat Flag Leaf in North China

Using a Li-6400 and Li-6400-40 Leaf Chamber Fluorometer(Li-Cor,Lincoln,NE,USA) portable photosynthesis open system,the CO₂ gas exchange and fluorescence measurements of different wheat varieties were conducted at different stages,CO₂ concentration and soil N content. The results showed that the light response curves and rapid light curves of wheat flag leaf were described well by the modified rectangular hyperbolic model. Meanwhile,the values of light saturated point were better matched to the measured data,and the values fitted with that estimated by the software of Photosynthesis. While the values,fitted by the software of Photosynthesi Assistant,were much lower. CO₂ concentration and soil N content had great effect on the light saturated point of wheat flag leaf. The light saturated point of wheat flag leaf significantly decreased at lower CO₂ concentration or lower soil N content. On the whole,the light saturated point of wheat flag leaf was between 1 700 and 2 000 mol·m^-2·s^-1,which was much higher than earlier results(1 200 mol·m^-2·s^-1). The results were in accordance with the sun leaves characters of wheat flag leaf and our practical observation.