Reference
Donnelly, A., Finnan, J., Jones, M.B. and Burke, J.I. 2005. A note on the effect of elevated concentrations of greenhouse gases on spring wheat yield in Ireland. Irish Journal of Agricultural and Food Research 44: 141-145.
What was done
Working at the Oak Park Research Center at Carlow, Ireland, the authors grew well watered and fertilized wheat (Triticum aestivum L.) plants from seed to maturity in pots recessed into the ground out-of-doors in open-top chambers in ambient air and air to which 90 ppb ozone (O3) was added at two different atmospheric CO2 concentrations: ambient (366 ppm) and elevated (681 ppm).
What was learned
Donnelly et al. report that "elevated O3 caused an overall reduction in both grain yield and the 1000-grain weight," but that "elevated CO2 produced an overall increase in grain yield, 1000-grain weight, number of ears and number of grains." In air of ambient O3 and CO2, for example, the grain yield of wheat was 2770 g/m2; but in the presence of the extra 90 ppb of ozone, the grain yield was cut to 1587 g/m2, or only 57% of what is was in ambient air. However, when the air's CO2 concentration was simultaneously increased (along with the O3 concentration), the grain yield of the wheat was raised to 2984 g/m2, which actually more than compensated for the deleterious effects of the extra ozone, boosting the grain yield to 8% above what it was in ambient air, and to fully 88% more than what it was in the O3-polluted ambient-CO2 air.
What it means
Donnelly et al.'s study indicates that ozone pollution can dramatically reduce the grain yield of wheat, but that atmospheric CO2 enrichment can just as dramatically reverse its adverse effects and actually lead to a modest increase in grain yield. Consequently, in the words of the researchers, "elevated CO2 can be seen as protecting some yield components from the damaging effects of O3," and that "the overall effect of increasing concentration of CO2 will be positive for wheat production in Ireland."