The latitudinal and altitudinal variations in the biochemical mechanisms of temperature dependence of photosynthesis within Fallopia japonica

The temperature dependence of the light-saturated rate of photosynthesis has large interspecific and intraspecific variations, which may be related to adaptation to the habitat environment. As both higher latitude and altitude have lower habitat temperature, we addressed the question of whether temperature adaptation is similar between high-latitude and high-altitude ecotypes. We raised three ecotypes of Fallopia japonica collected from high-latitude and low-altitude (Hirosaki), high-altitude and low-latitude (Fuji), and low-altitude and low-latitude (Tokyo) habitats at two growth temperatures, and determined the temperature dependence of photosynthesis and related biochemical and physical traits, including mesophyll conductance. Temperature dependence of photosynthesis and related traits differed among ecotypes, but the difference was not significant between Fuji and Tokyo when grown at a low-temperature. The simulation analysis suggested that the temperature dependence of Rubisco activity and the CO₂ concentration in the chloroplasts had large contributions to the variation in the temperature dependence of photosynthesis. We conclude that both ecotypes from high-altitude and high-latitude habitats tend to have a temperature dependence of photosynthesis which is adaptive to low-temperature conditions, but the mechanisms to adapt to high-altitude are not necessarily the same as compared with those to high-latitude.