Reference
Plessl, M., Heller, W., Payer, H.-D., Elstner, E.F., Habermeyer, J. and Heiser, I. 2005. Growth parameters and resistance against Drechslera teres of spring barley (Hordeum vulgare L. cv. Scarlett) grown at elevated ozone and carbon dioxide concentrations. Plant Biology 7: 694-705.
What was done
Well watered and fertilized spring barley (Hordeum vulgare L. cv. Scarlett) plants were grown from seed for four weeks after emergence in containers located within controlled-environment chambers maintained at either ambient (400 ppm) or 1.75 x ambient (700 ppm) atmospheric CO2 concentrations, while being simultaneously exposed to either ambient or 2 x ambient atmospheric O3 concentrations, after which the individual and combined effects of the CO2 and O3 additions were evaluated.
What was learned
Plessl et al. report that "elevated CO2 concentration significantly increased aboveground biomass [15%], root biomass [30%], and tiller number [41%], whereas double ambient ozone significantly decreased these parameters." When applied together, however, they say that the "ozone-induced reductions in growth parameters were strongly overridden by 700 ppm CO2." In fact, in the doubled ozone treatment, the 75% increase in the air's CO2 content increased the barley's aboveground biomass by 42%, its root biomass by 75%, and its tiller number by 94%.
What it means
In this particular study, a less than doubling of the air's CO2 concentration more than compensated for a full doubling of the air's O3 concentration, revealing the great potential for the ongoing rise in the air's CO2 content to not only overcome but even reverse the negative growth effects of elevated O3 concentrations on spring barley.