Responses of Soybean Cultivars to Elevated CO2 and O3.

The objective of our research is to measure soybean genetic variation for responses to increased CO2 and O3 concentrations under field conditions at the SoyFACE facility at the University of Illinois. Averaged over all cultivars and 5 years of testing from 2004 to 2008, elevated CO2 significantly delayed the onset of flowering, seed filling, and maturity, whereas elevated O3 significantly hastened each of these three growth stages. Elevated CO2 significantly increased plant height, lodging, seed weight and seed yield, and elevated O3 significantly reduced each of these traits. Although these general trends exist, there were differential responses among the cultivars for every trait measured including seed yield. Because the O3 treatment was relative to the ambient levels, average treatment levels varied from 53 to 71 ppb. Entries that are highly tolerant at the lower levels were not tolerant at the higher levels and the reverse is true for other cultivars. These results demonstrate that even among a relatively small sample of soybean cultivars it is possible to select for types that produce larger seed yield increases in elevated CO2 and smaller yield losses to elevated O3. The future response of the soybean crop to atmospheric changes will depend not only on the concentrations of CO2 and O3 but also on which cultivars are being grown. Genetic differences in responses to CO2 and O3 can be exploited by plant breeders to mitigate the losses to O3 and increase the gains from CO2.