Author
|
Submitted to: Oecologia
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 5/10/2000 Publication Date: N/A Citation: N/A Interpretive Summary: The concentration of carbon dioxide in the atmosphere is rising rapidly. One major impact of increasing atmospheric carbon dioxide is the stimulation of photosynthesis in most plants. The stimulation of photosynthesis at elevated carbon dioxide is expected to be negligible at low temperatures and to increase strongly with increasing temperature. This has potentially important implications for responses of crop plants t increasing atmospheric carbon dioxide. However, in this field study of Taraxacum officinale, there were no significant differences in the stimulation of photosynthesis by elevated carbon dioxide among days with temperatures ranging from 15 to 34 C. Nevertheless, field measurements of the short-term response to temperature were consistent with the expected strong temperature dependence of the stimulation of photosynthesis. This suggested that physiological adjustment to the prevailing temperature caused the lack of variation in the seasonal data. Experiments in controlled environments verified that this physiological adjustment to growth temperature occurred, and could account for the lack of response to seasonal temperature in the field data. These results indicate that it is premature to conclude that low temperatures will necessarily reduce the stimulation of photosynthesis caused by rising atmospheric carbon dioxide. This work has important implications for predictions of effects of rising atmospheric carbon dioxide on crops, and will be useful to modellers and crop physiologists preparing for global change conditions. Technical Abstract: The relative stimulation of photosynthesis by elevated carbon dioxide in C3 species normally increases strongly with increasing temperature. This results from the kinetic characteristics of Rubisco, and has potentially important implications for responses of vegetation to increasing atmospheric carbon dioxide. It is often assumed that because Rubisco characteristics are conservative, all C3 species have the same temperature dependence of the response of photosynthesis to elevated carbon dioxide. However, in this field study of Taraxacum officinale, there were no significant differences in the relative stimulation of photosynthesis by elevated carbon dioxide among days with temperatures ranging from 15 to 34 C. Nevertheless, short-term measurements indicated a strong temperature dependence of the stimulation. This suggested that acclimation to temperature caused the lack of variation in the seasonal data. Experiments sin controlled environments indicated that complete acclimation of the relative stimulation of photosynthesis by elevated carbon dioxide occurred for growth temperatures of 10 to 25 C. The apparent specificity of Rubisco for carbon dioxide relative to oxygen at 15 C, as assayed by in vivo measurements of the carbon dioxide concentration at which carboxylation equalled oxygenation, also varied with growth temperature. Changes in the apparent specificity of Rubisco accounted for the acclimation of the temperature dependence of the relative stimulation of photosynthesis by elevated carbon dioxide. It is premature to conclude that low temperatures will necessarily reduce the relative stimulation of photosynthesis caused by rising atmospheric carbon dioxide. |
