Background
The authors write that "few studies have been conducted in the field that quantified grapevine responses to elevated CO2," mentioning only Bindi et al. (1996, 2001a,b) and Bindi and Fibbi (2000). And they say that those researchers concluded that "doubled CO2 in the atmosphere results in strong stimulation of yield without having any negative or positive repercussion on grapes at maturity stage."

What was done
During the 2004, 2005 and 2006 growing seasons, Moutinho-Pereira et al. studied several characteristics of field-grown grapevines (Vitis vinifera L., cv. "Touriga Franca") in a vineyard located at Vila Real in the Baixo Corgo sub-region of the Demarcated Douro Region of Northern Portugal, where the plants were grown "using standard cultural decisions" -- but without irrigation -- within open-top chambers, with CO2 being supplied to half of them during daylight hours between the times of budbreak and harvest, which resulted in mean atmospheric CO2 concentrations over the growing season of 500 ppm compared to 365 ppm in the ambient-air chambers.

What was learned
It was determined that the experimentally-imposed -- and very modest -- 135-ppm increase in the atmosphere's CO2 concentration had a remarkable positive impact on the net photosynthetic rates of the grapevines, as well as their final yields, with the former being boosted by 56%, 26% and 18% in years 2004, 2005 and 2006, respectively, while the latter were increased by 50%, 27% and 50% in the same years.

What it means
Since the grape cultivar studied by Moutinho-Pereira et al. is said by them to be "universally recognized as the finest grape for Porto and red wine," we can only assume that their findings will be hailed as extremely good news by aficionados of the two beverages, especially since Goncalves et al. (2009) demonstrated in a companion study of the same grapevines that "the red wine quality remained almost unaffected" by the CO2 increase.

References
Bindi, M. and Fibbi, L. 2000. Modeling climate change impacts at the site scale on grapevine. In: Climate Change, Climate Variability and Agriculture in Europe, University of Oxford, Oxford, United Kingdom, pp. 117-134.

Bindi, M., Fibbi, L., Gozzini, B., Orlandin, S. and Miglieta, F. 1996. Modeling the impact of climate scenarios on yield and yield variability of grapevine. Climate Research 7: 213-224.

Bindi, M., Fibbi, L., Lanini, M., and Miglietta, F. 2001a. Free air CO2 enrichment (FACE) of grapevine (Vitis vinifera L.): I. Development and testing of the system for CO2 enrichment. European Journal of Agronomy 14: 135-143.

Bindi, M., Fibbi, L. and Miglietta, F. 2001b. Free air CO2 enrichment (FACE) of grapevine (Vitis vinifera L.): II. Growth and quality of grape and wine in response to elevated CO2 concentrations. European Journal of Agronomy 14: 145-155.

Goncalves, B., Falco, V., Moutinho-Pereira, J., Bacelar, E., Peixoto, F. and Correia, C. 2009. Effects of elevated CO2 on grapevine (Vitis vinifera L.): Volatile composition, phenolic content, and in vitro antioxidant activity of red wine. Journal of Agricultural and Food Chemistry 57: 265-273.