Effects of elevated carbon dioxide on photosynthesis and productivity of alfalfa in relation to seasonal changes in temperature

Authors: Bunce, James

Submitted to: Physiology and Molecular Biology of Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/21/2007
Publication Date: 12/1/2007
Citation: Bunce, J.A. 2007. Effects of elevated carbon dioxide on photosynthesis and productivity of alfalfa in relation to seasonal changes in temperature. Physiology and Molecular Biology of Plants. 13:243-252.

Interpretive Summary: The increase in plant growth with rising atmospheric carbon dioxide concentrations is expected to be larger at warm temperatures. We tested whether elevated carbon dioxide would shift the production of alfalfa toward warmer times of the year, which would benefit farmers by evening out cycles of hay production. This did not occur because of some unusual properties of photosynthesis in alfalfa. This work will be of interest to scientists predicting the effects of global climate change on crop production.

Technical Abstract: Alfalfa was grown at ambient and elevated (ambient + 350 ppm) carbon dioxide concentrations at Beltsville, Maryland, using open top chambers in field plots. Periodic harvests and measurements of leaf photosynthesis were used to test the hypothesis that the stimulation of yield and photosynthesis by elevated carbon dioxide would increase with temperature. There was no correlation between the relative or the absolute stimulation of yield at elevated carbon dioxide and the mean temperature during the re-growth interval. Short-term elevation of carbon dioxide for leaves of ambient-grown plants at different times of year increased their photosynthesis by an average of 1.5 fold, but there was no significant correlation between the relative stimulation of photosynthesis and temperature. Measurements of effects of short-term temperature treatments on the photosynthetic response to carbon dioxide showed that, unusually, photosynthetic rates measured at elevated carbon dioxide were not limited by carboxylation capacity but by maximum rates of electron transport. The limitation of photosynthesis by maximum electron transport rates caused the lack of temperature effects on the stimulation of photosynthesis by elevated carbon dioxide.