What was done
Spring wheat (Triticum aestivum L.) was grown in open-top chambers in the United Kingdom that were subjected to various atmospheric treatment combinations of CO2 (380 and 690 ppm) and O3 (27 and 61 ppb) to study the effects of these two trace gases on gas exchange in this species.

What was learned
Depending on the time of day and other environmental conditions, elevated CO2 increased photosynthetic rates by 43 to 67%.  Elevated CO2 also reduced stomatal conductance by about 50% relative to rates measured in leaves of ambiently-grown plants.  Elevated O3 severely reduced rubisco content in the youngest wheat leaves sampled.  However, leaves of plants exposed to both elevated CO2 and elevated O3 displayed no such reductions in leaf rubisco content, indicating that elevated CO2 ameliorated the negative effects of O3 on leaf rubisco content.  A similar ameliorating effect of elevated CO2 was observed for rubisco activity, which was decreased by elevated O3 under ambient CO2 conditions.

What it means
As the atmospheric CO2 concentration rises, it is likely that spring wheat plants will exhibit greater photosynthetic rates than they currently do under ambient CO2 concentrations.  Moreover, it is likely that rising CO2 concentrations will protect spring wheat plants from increasing O3 concentrations, which commonly reduce photosynthetic rates.  Indeed, this study demonstrates that elevated CO2 ameliorates elevated O3-induced reductions in rubisco activity and content.  In addition, CO2-induced reductions in stomatal conductance will likely allow this important agricultural crop to better cope with water stress through improved plant water-use.