What was done
The authors grew two potato species (Solanum curtilobum cv. Ugro Shiri, from high altitude, and S. tuberosum cv. Baronesa, from low altitude) in pots placed within open-top chambers maintained at atmospheric CO2 concentrations of 350 and 700 ppm for 30 days following the onset of reproductive growth to study the effects of elevated CO2 on gas exchange and biomass production in these two species of potato adapted to different altitudes.  To our knowledge, this is the first study of the CO2 responsiveness of the high-altitude-adapted Solanum curtilobum, which is economically important in the highlands of the South American Andes.

What was learned
Elevated CO2 increased rates of net photosynthesis by 56 and 53% in the high- and low-altitude potato species, respectively, while reducing their stomatal conductances by 55 and 59% and increasing their instantaneous water-use efficiencies by 90 and 80%, respectively.  It also increased tuber dry mass production by 85 and 40% in the high- and low-altitude potato species, respectively.

What it means
As the air's CO2 content continues to rise, both high- and low-altitude-adapted potato species will likely experience similar increases in their rates of photosynthesis, as well as similar reductions in their stomatal conductances, which should also lead to similar increases in their instantaneous water use efficiencies.  In the case of harvestable yield production, however, it appears that the response of the high-altitude potato species may be as much as twice as great as that of the low-altitude species.