What was done
Spring wheat (Triticum aestivum) was grown in FACE plots, located in Arizona, USA, at atmospheric CO2 concentrations of 370 and 550 ppm and two levels of soil moisture (50 and 100% of potential evapotranspiration) to determine the effects of elevated CO2 and soil moisture on leaf flavonoid concentrations.

What was learned
Leaves of plants grown in elevated CO2 had 14% higher total flavonoid concentrations than those of plants grown at the ambient CO2 concentration.  Similarly, leaves of plants grown at the optimum soil moisture content had flavonoid concentrations that were 11% greater than those observed in leaves of plants grown at less-than-optimal soil moisture contents.  However, there were no interactive effects of elevated CO2 and soil water content on leaf flavonoid concentrations.  Thus, elevated CO2 had a greater influence on leaf flavonoid concentrations than did soil moisture levels.

What it means
As the air's CO2 content rises, it is likely that flavonoid concentrations in wheat leaves will increase due to greater carbon availability resulting from enhanced photosynthetic rates.  These greater investments in leaf flavonoid concentrations will likely increase plant protection against UV-B radiation damage, which is one function of flavonoids in plant leaves.  It may also result in greater protection against herbivory by pests, as flavonoids are generally characterized as having anti-herbivory properties.  Thus, wheat yields will likely increase with future increases in the air's CO2 content, as wheat leaves will likely experience greater protection from both UV-B radiation and herbivory damage.