Analysis of the O2 dependency in leaf-level photosynthesis of two Reynoutria japonica populations growing at different altitudes

Abstract

To examine the effects of decreased CO2 and O2 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 O2 dependency of CE was significantly less in the highland population than in the lowland. Using theoretical analysis, we explained that O2 dependency of leaf-level photosynthesis became less as internal conductance (gi) decreased. We also showed that gi and the content of active Rubisco (E) could be estimated from the O2 dependency of leaf-level photosynthesis. By applying the analysis, a severe limitation of CO2 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 O2 dependency and photosynthetic capacity caused by a smaller gi in the highland population in addition to the differences in the partial pressures of CO2 and O2.