Elevated CO₂ significantly delays reproductive development of soybean under Free-Air Concentration Enrichment (FACE)
2009
Castro, Joseph C. | Dohleman, Frank G. | Bernacchi, Carl J. | Long, Stephen P.
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 (°Cd), 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 3 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.
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