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引种于青藏高原的大田玉米 ,在拔节期其净光合速率 (Pn)日变化为一单峰曲线 ,最大值 3 9. 0 3 μmol CO2 ·m- 2· s- 1出现在 1 5:0 0 ;而文献中生长在干旱半干旱交错平原区的同品种玉米 , Pn日变化为双峰曲线 ,最大值 2 0 . 0 3μmol CO2 · m- 2· s- 1出现在 1 2 :0 0。表明玉米从低海拔平原引种到高海拔地区使叶片净光合速率变大。适宜的白天高温、充足的太阳光能和水分供应是出现这一变化的主要原因 ;而且引种玉米叶片的光饱和点与光补偿点均增大 ,认为这是对高原环境强烈光照的一种适应。另外 ,玉米叶片细胞间隙 CO2 浓度并非象某些文献所报道是保持不变 ,而是在全天进程中有起伏波动
The net photosynthetic rate (Pn) diurnal variation of field maize introduced to the Qinghai-Tibet Plateau was a single peak curve with the maximum value of 39.09 μmol · m-2 · s-1 at 15: 0 0 In the literature, the diurnal variation of Pn was the same for maize grown in arid and semi-arid crisscross plain areas. The maximum value of 20.0 μmol · m-2 · s-1 appeared at 12: 0 0. The results showed that the introduction of maize from low-altitude plain to high altitude increased the net photosynthetic rate of leaves. Suitable daytime high temperature, adequate sunlight energy and water supply are the main reasons for this change; and the light saturation point and light compensation point of introduced maize leaves are both increased, which is considered to be a kind of adaptation to strong sunlight in plateau environment . In addition, the intercellular CO2 concentration in maize leaves is not as constant as reported in some literature, but fluctuates throughout the day