ARS | Publication request: How will soybeans respond to elevated temperatures when grown at future CO2 concentrations under fully open air field conditions (FACE)?

Submitted to: Plant Biology Annual Meeting
Publication Type: Abstract
Publication Acceptance Date: May 15, 2008
Publication Date: June 23, 2008
Citation: Rosenthal, D.M., Bernacchi, C.J., Zhu, X., Ort, D.R. 2008. How will soybeans respond to elevated temperatures when grown at future CO2 concentrations under fully open air field conditions (FACE)? [abstract]. American Society of Plant Biologists Annual Meeting. Paper No. P20009. Available: http://abstracts.aspb.org/pb2008/public/P20/P20009.html.

Technical Abstract: Elevating CO2 and temperature both influence plant productivity through their direct effects on photosynthesis. This is true because O2 and CO2 compete for same active sites of ribulose bisphophate carboxylase-oxygenase (rubisco). Increasing temperature increases oxygenation relative to carboxylation because the solubility of O2 increases and the specificity of rubisco for CO2 decreases. However, increasing CO2 relative to CO2 will always increase carboxylation:oxygenation so net inhibition of oxygenation will have the greatest effect at higher temperatures. The implication is that the temperature optimum (Topt) of photosynthesis will be higher in a warmer elevated CO2 world creating a positive feedback on photosynthesis in the future. A number of growth chamber and pot studies have examined these effects separately and in combination. Some show increased productivity or Topt in response to elevated temperature and CO2. These results, however, should be evaluated cautiously since recent meta-analyses have demonstrated that pot and chamber studies tend to overestimate the impact of elevated CO2 on productivity when compared to fully open air CO2 enrichment studies (FACE). Further, the temperature response of photosynthesis may be confounded by increases in leaf temperature due solely to elevated CO2 effects on stomatal conductance (gs) because elevated CO2 reduces gs which in turn reduces evapotranspiration. In fact, mean canopy temperature and daily temperature range (DTR) in plots with elevated CO2 at SoyFACE are significantly higher than ambient plots. Whether or not increases in mean leaf temperature due to decreased stomatal conductance or the frequency of temperature excursions above Topt lead to a feedback on productivity remains an open question.