What was done
Tall fescue (Festuca arundinacea) plants were grown for two weeks in open-top chambers receiving atmospheric CO2 concentrations of 350 and 700 ppm before being inoculated with aphids (Rhopalosiphum padi) at a density of 20 individuals per plant.  After nine additional weeks of differential CO2 treatment, plants were harvested and their associated aphids were counted, to determine the effects of elevated CO2 on plant and aphid growth.

What was learned
Although elevated CO2 increased plant dry matter production by 37%, this phenomenon did not result in similar increases in aphid colonization.  In fact, plants grown in elevated CO2 contained 322% fewer aphids than plants grown at ambient CO2.  Similarly, aphid densities on CO2-enriched plants were 467% lower than those measured on plants grown at 350 ppm CO2.

What it means
As the atmospheric CO2 concentration increases, it is likely that Tall fescue plants will respond by increasing their biomass.  However, the likely increases in carbohydrates responsible for this phenomenon should not increase the populations of bird cherry-oat aphids associated with this species.  Indeed, the rising CO2 content of the air should actually decrease the association of this aphid with this plant species, thus allowing Tall fescue to respond even better to increasing concentrations of this trace gas.