What was done
The authors grew potatoes (Solanum tuberosum L.) in open-top chambers receiving atmospheric CO2 concentrations of 380, 550 and 680 ppm.  In addition, chambers were fumigated with air containing ambient and elevated levels of ozone (O3).  Thus, the authors studied the interactive effects of elevated CO2 and ozone on gas exchange in this important agricultural crop.

What was learned
Overall, elevated CO2 had a greater effect on gas exchange than did elevated ozone.  Plants grown at 680 ppm CO2, for example, exhibited stomatal conductances that were 62 and 47% lower than those displayed by plants growing at 380 ppm CO2 while exposed to ambient and elevated concentrations of ozone, respectively.  Neither elevated CO2 nor ozone impacted rates of carbon fixation to any significant degree, except for plants growing at 550 ppm CO2 and ambient ozone, where there was an 80% increase in net photosynthesis due to atmospheric CO2 enrichment.  Nevertheless, elevated CO2 progressively increased instantaneous water use efficiency, regardless of ozone exposure.

What it means
As the air's CO2 content rises, potatoes will likely display an increase in their water-use efficiency, due in part to reductions in stomatal conductance and increases in rates of net photosynthesis.  Thus, it is likely that potatoes will be able to better deal with water stress in the future.  In addition, it is also possible that potatoes could be grown in more arid regions if the air's CO2 content rises.