What was done
The authors grew peanuts (Arachis hypogaea L., cv NC-V11) in a field near Raleigh, North Carolina (USA) using standard agricultural practices for two years in open-top chambers maintained at all combinations of three CO2 treatments (375, 548 and 730 ppm) and three O3 treatments -- charcoal-filtered air (CF, 22 ppb), non-filtered air (NF, 46 ppb) and O3-enriched air (75 ppb) -- after which peanut seed yields and qualities were assessed.

What was learned
Burkey et al. report that "elevated CO2 increased yield parameters 7 to 17% for plants grown in CF air and restored yield in NF air and elevated O3 treatments to control or higher [our italics] levels," while "market grade characteristics and seed protein and oil contents were not affected by elevated O3 and CO2."

What it means
The USDA Agricultural Research Service scientists conclude that, in the case of peanuts, "the major impacts of rising atmospheric O3 and CO2 will be on productivity, not product quality," and in the area of productivity, their data indicate that the positive effects of the ongoing rise in the air's CO2 content should be able to compensate for concomitant future increases in tropospheric ozone concentrations. In fact, the continuing upward trend in atmospheric CO2 concentration should more than compensate for any future increases in the air's O3 content, because the latter will likely be relatively small due to the strong negative influence of elevated atmospheric CO2 concentrations on vegetative isoprene emissions (Monson et al., 2007), which are responsible for increasing O3 concentrations over land by perhaps 50% over what they would be in their absence (Poisson et al., 2000), as has been demonstrated by Arneth et al. (2007), who have calculated that when the effect of CO2 on vegetative isoprene emissions is included, a properly-forced model "maintains global isoprene emissions within ± 15% of present values," which should significantly temper the future rate-of-rise of the troposphere's ozone concentration.

References
Arneth, A., Miller, P.A., Scholze, M., Hickler, T., Schurgers, G., Smith, B. and Prentice, I.C. CO2 inhibition of global terrestrial isoprene emissions: Potential implications for atmospheric chemistry. Geophysical Research Letters 34: 10.1029/2007GL030615.

Monson, R.K., Trahan, N., Rosenstiel, T.N., Veres, P., Moore, D., Wilkinson, M., Norby, R.J., Volder, A., Tjoelker, M.G., Briske, D.D., Karnosky, D.F. and Fall, R. 2007. Isoprene emission from terrestrial ecosystems in response to global change: minding the gap between models and observations. Philosophical Transactions of the Royal Society A 365: 1677-1695.

Poisson, N., Kanakidou, M. and Crutzen, P.J. 2000. Impact of non-methane hydrocarbons on tropospheric chemistry and the oxidizing power of the global troposphere: 3-dimensional modeling results. Journal of Atmospheric Chemistry 36: 157-230.