What was done
The authors grew spring wheat (Triticum aestivum L. cv. Dragon) in open-top chambers located in Ostad, Sweden, at atmospheric CO2 concentrations of 340 and 680 ppm for three consecutive years.  In addition, they exposed some plants in each CO2 treatment to ambient, 1.5 x ambient and 2 x ambient concentrations of atmospheric O3 (ozone) to determine the interactive effects of elevated CO2 and O3 concentrations on spring wheat growth.  In addition, in the final year of the study, irrigation water was applied at normal or high amounts to determine if additional soil moisture would influence plant growth responses to elevated CO2 and O3 concentrations.

What was learned
Elevated soil moisture had little influence on wheat yield, regardless of atmospheric CO2 and O3 concentrations.  Elevated O3 concentrations, however, negatively influenced wheat yield at both atmospheric CO2 concentrations.  Nevertheless, grain yield was always higher for plants grown at the elevated CO2 concentration.  Indeed, elevated CO2 increased grain yield by 21, 7 and 11%, respectively, for each of the three years of the study, indicating that elevated CO2 concentrations ameliorated some of the negative impacts of O3-induced damage on grain yield.

What it means
As the air's CO2 - and probably its O3 - concentration continue to rise, spring wheat yields in Nordic countries will likely increase, due to the CO2-induced amelioration of O3-induced reductions in photosynthesis, growth and yield, plus the direct positive effects of elevated CO2 on wheat photosynthesis, growth and yield.  In fact, in their concluding remarks the authors state that "the positive effect of elevated CO2 could compensate for the yield losses due to O3."  Thus, it is likely that wheat farmers in this part of Europe can expect future increases in grain production as the CO2 content of the air continues to rise.