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

为探讨CO_2和O_2分压降低对高山植物叶片光合作用的影响，比较了高海拔地区日本野蕨（Escherichia japonica Houtt.）变种一种生长在高地，另一种生长在低地。高原种群在自然大气条件下的CE显著低于低地种群。在高原地区，CE的O_2依赖性显著低于低地。通过理论分析，我们解释了叶片光合作用的O_2依赖性随内电导（g_1）的降低而降低。我们还发现，g_1和活性Rubisco（E）的含量可以从叶片光合作用的O_2依赖性来估计。结果表明，高原种群的CO_2扩散受到严重限制，而两种群的E值几乎相同。对这种差异的合理解释是，高原种群的gI较小，对O_2的依赖性和光合能力较小，CO_2分压和O_2分压也有差异。

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.