What was done
The authors grew two spring wheat (Triticum aestivum L.) cultivars of varying drought sensitivity (cv. Longchun 292, more tolerant, and 8139, less tolerant) in environmental chambers receiving atmospheric CO2 concentrations of 350 and 700 ppm to study the effects of elevated CO2 on drought tolerance in these closely related cultivars.

What was learned
Prior to drought stress, foliar concentrations of the highly reactive oxygenated compound H2O2 were similar in both cultivars, regardless of atmospheric CO2 concentration.  After the induction of water stress in ambient air, however, levels of H2O2 began to slowly increase over a five- and six-day day period in cultivars 8139 and 292, respectively, prior to the start of the more rapid increases that occurred after this first stage of minimal response.  In contrast, under elevated CO2 concentrations, levels of H2O2 slowly increased over an eight-day period in both cultivars prior to the start of the more rapid increases, thus indicating a significant CO2-induced delay in the onset of the major period of water stress-induced production of this powerful oxidizing compound.  In addition, plants grown in elevated CO2 maintained higher enzymatic activities of superoxide dismutase and catalase - two important antioxidants - relative to those observed in ambiently-grown plants, following the induction of water stress.

What it means
As the CO2 concentration of the atmosphere increases, the specific spring wheat cultivars of this study will likely become more adept at dealing with water stress.  Indeed, elevated CO2 levels should reduce the amount of active oxidizing compounds present in leaves, while simultaneously enhancing the ability of antioxidizing enzymes to remove them.  In addition, it is interesting to note that in this case, the less drought resistant cultivar 8139 experienced a greater CO2-induced improvement in delaying water stress than the more drought resistant cultivar 292.  Thus, elevated CO2 may well have a greater impact on increasing drought resistance in inherently less drought tolerant species than it does in more drought tolerant species, i.e., it may help those plants most that need the most help.