Submitted to: Journal of Experimental Botany
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/1/2009
Publication Date: 6/26/2009
Citation: Castro, J.C., Dohleman, F.G., Bernacchi, C.J., Long, S.P. 2009. Elevated CO2 Significantly Delays Reproductive Development of Soybean Under Free-Air Concentration Enrichment (FACE). Journal of Experimental Botany. 60(10):2945-2951. Interpretive Summary: We have previously shown that plants grown in concentrations of CO2 predicted for mid-way through this century will use less water and this will result in warmer plant canopies. It is well known that there exists a strong link between growth temperatures and development in many plant species. One of the potential consequences of the warmer temperature associated with growth in elevated CO2 is that plants would mature faster. We set out to determine whether the higher canopy temperature associated with increased CO2 would accelerate development for soybean grown at the Soybean Free Air CO2 Enrichment facility in Champaign, IL. We used measurements of canopy temperature with measures of plant growth and reproductive stages to quantify the number of growing degree days (GDD) required to achieve each of the developmental stages. While that canopies were warmer for the elevated CO2 plots, we found that the number of GDD required to hit each of the developmental stages were less than in the control. This was the opposite of what we expected and these results suggest that direct effects of CO2 on plant development can have impacts on projected grain yield in the future. Assuming other species, agronomic and natural, have similar responses suggests that future atmospheric conditions can have large impacts on both managed and natural communities.
Technical Abstract: The effect of rising atmospheric concentration of carbon dioxide [CO2] on the reproductive development of soybean (Glycine max. Merr) has not been evaluated under open-air field conditions. Soybeans grown under Free Air CO2 Enrichment (FACE) exhibit warmer canopies due to decreased latent heat loss because of decreased stomatal conductance. According to development models based on accumulated thermal time, or growing degree days (GDD), increased canopy temperature should accelerate development. The SoyFACE research facility (Champaign, Illinois, USA) was used to test the hypothesis that development is accelerated in soybean when grown in [CO2] elevated to 548 µmol mol-1. Canopy temperature was measured continuously with infrared thermometry, and used in turn to calculate GDD. Opposite to expectation, elevated [CO2], while increasing canopy temperature, delayed reproductive development by up to three days (p<0.05). Soybean grown in elevated [CO2] required ~49°Cd more GDD (p<0.05) to complete full bloom stage (R2) and ~52°Cd more GDD (p<0.05) to complete the beginning seed (R5) stage, but needed ~46°Cd fewer GDD (p<0.05) to complete seed filling (R6). Soybeans grown in elevated [CO2] produced significantly more nodes (p<0.01) on the main stem than those grown under current [CO2]. This may explain the delay in completion of reproductive development and final maturation of the crop under elevated [CO2]. These results show a direct effect of rising [CO2] on plant development that will affect both projections of grain supply and may be significant to other species including those in natural communities.