What was done
For one complete growing season, the authors raised potatoes within open-top chambers maintained at either ambient or elevated (ambient + 350 ppm) atmospheric CO2 concentrations under normal field conditions in the subarctic environment of Fairbanks, Alaska, USA, making various physiological measurements during the growth period and determining the final state of the plants at harvest, which was conducted the day after the first killing frost.

What was learned
During the period of tuber development, net photosynthetic rates in the elevated-CO2 chambers were 53% greater than those in the ambient-air chambers; and at final harvest, tuber biomass was 36% greater in the CO2-enriched chambers compared to the ambient-air chambers. However, there were decreases in tuber reducing sugars (20% for sucrose and 30% for glucose).

What it means
With respect to the tuber biomass response, and citing the work of Idso et al. (1987), Conn and Cochran note that the low temperatures characteristic of Fairbanks may have actually limited the response of the Alaska potato crop to the extra CO2 to which the plants were exposed, which suggests that in warmer regions the growth response may have been even greater. With respect to the tuber sugar response, they say that "high reducing sugar content is responsible for producing overly dark colors when tubers are fried in oil at high temperatures with the result that tubers with high levels of reducing sugars cannot be used for making fries or chips (Sowokinos and Preston, 1988)." Hence, they conclude that "the declines in reducing sugars found in this study resulting from elevated atmospheric CO2 are of practical benefit to potato growers in Alaska and elsewhere where tuber reducing sugar content is high."

References
Idso, S.B., Kimball, B.A., Anderson, M.G. and Mauney, J.R. 1987. Effects of atmospheric CO2 enrichment on plant growth: the interactive role of air temperature. Agriculture, Ecosystems and Environment 20: 1-10.

Sowokinos, J.R. and Preston, D.A. 1988. Maintenance of Potato Processing Quality by Chemical Maturity Monitoring (CMM). Bulletin 586. Minnesota Agricultural Experiment Station. University of Minnesota, St. Paul, Minnesota, USA.