What was done
The authors grew potatoes (Solanum tuberosum L.) in open-top chambers receiving atmospheric CO2 concentrations of 350, 550 and 680 ppm in combination with ambient (30 ppb) or elevated (60 ppb) O3 (ozone) concentrations to determine the interactive effects of these variables on potato tuber yield.

What was learned
Elevated ozone did not affect tuber yield, regardless of atmospheric CO2 concentration; and it did not interact significantly with elevated CO2.  Early on, elevated CO2 significantly increased both total plant and tuber dry weight.  Tuber weight shortly after tuber initiation, for example, was 2.2-fold greater at 550 and 680 ppm than it was at 350 ppm CO2.  However, at final harvest total tuber dry weight was unaffected by elevated CO2, even though CO2-enriched plants produced 25% more tubers.

What it means
This study is one of the few that show no significant yield response to elevated CO2 exposure in a C3 crop species.  Moreover, it differs dramatically from earlier reports of significant CO2-induced yield increases in potato (Miglietta et al., 1998; Sicher and Bunce, 1999).  The authors are very careful in discussing this fact and suggest that differing experimental locations, environmental conditions and/or potato varieties may have led to their observed inconsistencies in yield response.  Nonetheless, it is important to note that these authors did not find a negative effect of elevated CO2 on potato yield, but simply no effect.

References
Miglietta, F., Magliulo, V., Bindi, M., Cerio, L., Vaccari, F.P., Loduca, V. and Peressotti, A.  1998.  Free Air CO2 Enrichment of potato (Solanum tuberosum L.): Development, growth and yield.  Global Change Biology 4: 163-172.

Sicher, R.C. and Bunce, J.A.  1999.  Photosynthetic enhancement and conductance to water vapor of field-grown Solanum tuberosum (L.) in response to CO2 enrichment.  Photosynthesis Research 62: 155-163.