西藏高原田间冬小麦旗叶光合作用研究

 西藏高原冬小麦旗叶光合速率日变化曲线为平坦或单峰型，没有明显“午睡”现象。净光合速率日最高值可与平原接近。光合日总量最高值出现在灌浆中期，其值比平原低4％～34％。净光合速率达20μmolCO2·m-2·s-1以上的环境因子组合是光合有效辐射光量子通量密度2000μmol·m-2·s-1以上，气温25～29℃，近地层大气CO2密度0.41mg·dm-3以上，0cm地温18～23℃、5cm地温15～19℃。这样的因子组合在高原同时满足的机率不高，由于CO2浓度与光温因子高值出现时间不同步，更由于CO2密度比内陆平原低1/3，严重制约了光合日总量值，高原冬小麦旗叶光合作用的特点是净光合速率日最高值可与平原接近，但光合日总量却明显低于平原。

FLAG LEAF PHOTOSYNTHESIS OF WINTER WHEAT ON A FARMLAND OF TIBET PLATEAU

Diurnal variation curve of net photosynthetic rate (Pn) of flag leaf of winter wheat in farmland of Tibet plateau was flat one or with one single peak, having hardly midday depression of Pn. Daily maximum of Pn was near to approach that observed in the east plain of China. The peak of the daily total amount of Pn is about 66%～96% of that in the plain. In Tibet plateau, the environmental conditions which enable the flag leaf of the plant to have Pn higher than 20μmol CO2·m-2·s-1 were the following : PFD was higher than 2000μmol·m-2·s-1, Ta was 25～29℃, ambient CO2 density was higher than 0.41mg·dm-3. Soil surface temperature was 18～23℃ ,and underground temperature (5cm depth) was 15～19℃. Probability at which suchlike factors combination occurs was not high. Ambient CO2 density was about one third lower than that in the plain. It restricted the daily total amount of Pn. Flag leaf of the plant in Tibet plateau had daily maximum of Pn approach similar to that in the plain, but its daily total amount of Pn was lower than that in the plain. Photosynthetic capabilities were high, but sunlight utilization efficiency was low.