The ratio of the capacities of ribulose-1,5-bisphosphate (RuBP) regeneration to RuBP carboxylation (Jmax/Vcmax) (measured at a common temperature) increases in some species when they are grown at lower temperatures, but does not increase in other species. To investigate the mechanism of interspecific difference in the response of Jmax/V cmax to growth temperature, we analysed the temperature dependence of Vcmax and Jmax in Polygonum cuspidatum and Fagus crenata with the Arrhenius function. P. cuspidatum had a higher ratio of J max/Vcmax in spring and autumn than in summer, while F. crenata did not show such change. The two species had a similar activation energy for Vcmax (EaV) across seasons, but P. cuspidatum had a higher activation energy for Jmax (EaJ) than F. crenata. Reconstruction of the temperature response curve of photosynthesis showed that plants with an inherently higher EaJ/EaV (P. cuspidatum) had photosynthetic rates that were limited by RuBP regeneration at low temperatures and limited by RuBP carboxylation at high temperatures, while plants with an inherently lower EaJ/EaV (F. crenata) had photosynthetic rates that were limited solely by RuBP carboxylation over the range of temperatures. These results indicate that the increase in J max/Vcmax at low growth temperatures relieved the limitation of RuBP regeneration on the photosynthetic rate in P. cuspidatum, but that such change in Jmax/Vcmax would not improve the photosynthetic rate in F. crenata. We suggest that whether or not the J max/Vcmax ratio changes with growth temperature is attributable to interspecific differences in EaJ/EaV between species.
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