Response of respiration of soybean leaves grown at ambient and elevated carbon dioxide concentrations to day-to-day variation in light and temperature under field conditions

Authors: Bunce, James

Submitted to: Annals of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2005
Publication Date: 3/21/2005
Citation: Bunce, J.A. 2005. Response of respiration of soybean leaves grown at ambient and elevated carbon dioxide concentrations to day-to-day variation in light and temperature under field conditions. Annals of Botany. 95:1059-1066.

Interpretive Summary: The concentration of carbon dioxide in the atmosphere is rising rapidly, with potentially important effects on plants. Plants respire, and how much they respire affects their growth, but it is uncertain how respiration will respond to increases in atmospheric carbon dioxide concentration, and there are few measurements of respiration for crop plants grown at elevated carbon dioxide under field conditions. It was expected that increased photosynthesis caused by growth at elevated carbon dioxide would lead to increased respiration. In this study, photosynthesis and respiration were recorded for whole days for mature leaves of soybeans grown in field plots at the current ambient carbon dioxide concentration and at 350 ppm above ambient. Elevated carbon dioxide increased daytime net photosynthesis by an average of 50%, but had no effect on night time respiration, which is contrary to expectations. This information will be of use to scientists predicting responses of crops to rising atmospheric carbon dioxide concentrations.

Technical Abstract: Respiration is an important component of plant carbon balance, but it remains uncertain how respiration will respond to increases in atmospheric carbon dioxide concentration, and there are few measurements of respiration for crop plants grown at elevated carbon dioxide under field conditions. Net rates of carbon dioxide exchange were recorded 24 h per day for mature upper canopy leaves of soybeans grown in field plots at the current ambient carbon dioxide concentration and at ambient plus 350 ppm in open top chambers. Daily photosynthesis, temperature, and leaf dry mass per unit of area were examined for effects on respiration. Measurements were made on pairs of leaves from both carbon dioxide treatments on each of 16 days during the middle of the growing seasons of two years. Elevated carbon dioxide increased daytime net carbon dioxide fixation rates per unit of leaf area by an average of 50%, but had no effect on night time respiration expressed per unit of area. Respiration per unit of mass was significantly lower (23%) at elevated carbon dioxide. Respiration increased with average night temperature, increasing by a factor of 2.5 between 18 and 26 C for both carbon dioxide treatments. These results do not support the hypotheses that elevated carbon dioxide would increase respiration per unit of area by increasing photosynthesis or leaf mass per unit of area, or that acclimation of respiration to temperature would be rapid enough to make dark respiration insensitive to variation in temperature among nights.