Acclimation to temperature of the response of photosynthesis to increased carbon dioxide concentration in Taraxacum officinale

The relative stimulation of photosynthesis by elevated carbon dioxide in C- 3 species normally increases strongly with increasing temperature. This res ults from the kinetic characteristics of Rubisco, and has potentially impor tant implications for responses of vegetation to increasing atmospheric car bon dioxide. It is often assumed that because Rubisco characteristics are c onservative, all C-3 species have the same temperature dependence of the re sponse of photosynthesis to elevated carbon dioxide. However, in this field study of Taraxacum officinale, there were no significant differences in th e relative stimulation of photosynthesis by elevated carbon dioxide among d ays with temperatures ranging from 15 to 34 degreesC. Nevertheless, short-t erm measurements indicated a strong temperature dependence of the stimulati on. This suggested that acclimation to temperature caused the lack of varia tion in the seasonal data. Experiments in controlled environments indicated that complete acclimation of the relative stimulation of photosynthesis by elevated carbon dioxide occurred for growth temperatures of 10 - 25 degree sC. The apparent specificity of Rubisco for carbon dioxide relative to oxyg en at 15 degreesC, as assayed in vivo by measurements of the carbon dioxide concentration at which carboxylation equalled oxygenation, also varied wit h growth temperature. Changes in the apparent specificity of Rubisco accoun ted for the acclimation of the temperature dependence of the relative stimu lation of photosynthesis by elevated carbon dioxide. It is premature to con clude that low temperatures will necessarily reduce the relative stimulatio n of photosynthesis caused by rising atmospheric carbon dioxide.