Explication of leaf-level acclimations and adaptation to the low atmospheric pressure at high altitude

为了研究CO2和O2分压降低对高原高山植物叶片光合作用的影响，比较了高寒植物红毛菊的最大羧化效率CE。瓦尔一种生长在高地，一种生长在低地。在自然大气条件下，高原种群的CE显著低于低地种群。高原人群CE对氧的依赖程度明显低于低地人群。通过理论分析，我们解释了叶片水平光合作用对O2的依赖程度随内导度(GI)的降低而减小。根据叶片水平光合作用对O2的依赖关系，可以估算出gI和活性Rubisco含量(E)。结果表明，高原居群的CO2扩散受到严重限制，而两个居群的E值基本相同。对这种差异的合理解释是，除了CO_2和O_2分压的差异外，高原种群对O_2的依赖性和光合作用能力较小。

To examine the effects of decreased CO_2 and O_2 partial pressure on leaf-level photosynthesis in alpine plants at high altitude, we compared the maximal carboxylation efficiency CE, of Reynoutria japonica Houtt. Var. japonica growing in a highland with one growing in a lowland. CE under the native atmospheric conditions (native CE) of the highland population was significantly lower than that of the lowland one. The O_2 dependency of CE was significantly less in the highland population than in the lowland. Using theoretical analysis, we explained that O_2 dependency of leaf-level photosynthesis became less as internal conductance (g_I) decreased. We also showed that g_I and the content of active rubisco (E) could be estimated from the O_2 dependency of leaf-level photosynthesis. By applying the analysis, a severe limitation of CO_2 diffusion in the leaf was estimated in the highland population whereas almost the same values of E were estimated in both populations. A reasonable explanation for the difference in the native CE is the smaller O_2 dependency and photosynthetic capacity caused by a smaller g_I in the highland population in addition to the differences in the partial pressures of CO_2 and O_2.