What was done
Soybean plants were grown for one season in pots within open-top chambers receiving atmospheric CO2 concentrations of 370, 482, 599, and 713 ppm in combination with atmospheric O3 (ozone) concentrations of 20, 50, and 79 ppb to study the interactive effects of these variables on soybean biomass.

What was learned
By harvest time (113 days after planting), elevated CO2 had significantly increased all biomass and growth variables measured, with the greatest percentage enhancements typically occurring at the highest CO2 and O3 concentrations.  Plants grown at 20 ppb O3 and 713 ppm CO2, for example, displayed total dry weights that were 48% greater than their ambiently-grown counterparts, while plants grown at 79 ppb O3 and 713 ppm CO2 exhibited dry weights that were 53% greater than their respective controls.

On an absolute scale, plants grown in ambient CO2 with 79 ppb O3 displayed a 26% reduction in total dry weight when compared with plants grown at 20 ppb O3.  However, plants grown at 713 ppm CO2 with 79 ppb O3 exhibited a mere 12% reduction in dry weight relative to their controls subjected to 20 ppb O3, which is half that experienced by plants grown in ambient CO2.  Thus, growth in a "doubled" CO2 atmosphere nearly completely suppressed the negative effects of high O3-induced stress on biomass production.

What it means
As the air's CO2 and O3 contents continue to rise, it is likely that soybeans will experience reduced deleterious effects resulting from O3-induced stresses, particularly when the CO2 content approximately doubles that of its present level.  Moreover, it is conceivable that other plants will mimic the response of soybean to elevated CO2 and experience less damage from this aerial pollutant as the atmospheric CO2 concentration rises ever higher.