What was done
The authors grew single-node explants of sweet potato (Ipomoea batatas cv. Naruto Kintok) for five weeks in vitro within special culture vessels supplied with a 3% sugar-containing agar, during which period the vessels were maintained at atmospheric CO2 concentrations of either 400 ppm (ambient) or 1000, 2000 or 3000 ppm, after which the plants were transplanted into soil and grown ex vitro for three additional weeks.

What was learned
Relative to the plants exposed to ambient air, those exposed to air of 1000, 2000 and 3000 ppm CO2 produced 20%, 20% and 65% more total biomass, respectively, after having been grown for five weeks in vitro, while they produced 20%, 32% and 82% more biomass, respectively, after having been grown for three additional weeks ex vitro.

What it means
For sweet potato plants, as well as the many other plants that have been similarly studied (see both Aquatic Plants and Terrestrial Plants under Growth Response to Very High CO2 Concentrations in our Subject Index), several-fold increases in the atmosphere's CO2 concentration appear to pose no problem to the plants' growth and development. In fact, the more CO2 there has been in the air during these studies, the more biomass the tested plants have typically produced.