散射光和直射光对高粱叶片光合功能的影响

C₄等面叶作物背腹侧结构相似并分别暴露在散射光和直射光下。为阐述散射光和直射光对其光合功能的驱动作用，以高粱为材料，研究了散射光和直射光对叶片背腹侧光合功能的影响。结果表明,高粱叶片背腹侧解剖结构相似，其光谱学特性差异很小, 与近轴侧相比，远轴侧的气孔密度、气孔下腔面积、维管束鞘细胞与叶肉细胞接触面积较大; 在相同直射光下近、远轴侧均具有较高的光合速率, 在近轴侧照光同时用PE膜封闭叶片受光侧气孔，观察到远轴侧在叶片自身透射光下能够维持较高的净光合速率；相反，近轴侧在自身透射光下光合速率很低; 自然光照条件下一天内直射光和散射光强度差异很大，大部分时间的散射光强度明显低于远轴侧光补偿点。由此认为，高粱远轴侧光合作用主要由自身透射光驱动，散射光作用很小，该特性是对光环境的适应。这对田间等面叶作物生产管理、生态系统生产力的研究和高光效育种有重要意义。

Effects of Diffuse and Direct Light on Photosynthetic Function in Sorghum Leaf

The effects of direct and diffuse light on the leaf-side-specific regulation of photosynthesis were studied in sorghum,a typical C4 plant.Leaf morphology and structure were carefully investigated by semithin cross section of sorghum leaves.Leaf absorption,transmittance and reflectance profiles were similar on the adaxial and abaxial leaf surfaces across the light spectrum from 400 to 800 nm,whether light was illuminated via the adaxial or abaxial surface.The photosynthetic light-response curves showed that the maximal whole photosynthetic rate was higher when the light entered the leaf via the adaxial surface than the abaxial surface.The changing trend of stomatal conductance was similar with photosynthetic light-response curves.However,the maximal photosynthetic rate was much lower when the light entered the leaf via the abaxial surface than adaxial surface when blocking the stomata of light-oriented side by PE membrane.The intensity of direct and diffuse lights varied widely in a day,and that of diffuse light was significantly lower than light compensate point(Ic) of abaxial leaf surfaces in sorghum.Consequently,photosynthetic rate of abaxial leaf surface in sorghum should be mainly droved by self-transmitted light but not diffuse light.Differences in stomatal density,substomatic cavity,contacting areas between bundle sheath and mesophyll cells are related to this feature of abaxial leaf surfaces.The findings of the present study are important for field management,investigation of ecosystem productivity and breeding for high photosynthetic efficiency.