Sweet potato shows strong growth under high atmospheric CO2 concentrations

Sweet potatoes (Ipomoea batatas) are set to play an important role in the emerging 'carbohydrate economy' (previous post). The starch-rich root crop is already being used for the production of liquid biofuels and biogas as well as for bioplastics.

The Chinese government, which recently put a moratorium on the use of corn for biofuels, has officially named sweet potato as a crop of preference for the production of ethanol instead (more here). Auto manufacturer Toyota has a large plantation of the tuber in Indonesia to make bioplastics from it. Researchers are also looking into using the crop for the production of biohydrogen.

The starchy batatas may help us manufacture carbon-neutral bioproducts that replace petroleum, but in any case carbon dioxide emissions from burning fossil fuels are expected to keep increasing for decades to come. For this reason, scientists find it important to understand the effects of these emissions on the growth of plants (earlier post). As they have done for many other crops, researchers are trying to find out what will happen to the metabolism of sweet potatos under increased atmospheric CO2 conditions.

Writing in the Journal of Plant Biotechnology, Teixeira da Silva and team report results of trials with the tuber. They found significally increased biomass growth in the crop when it was exposed to increased levels of CO2.

The authors grew single-node explants of sweet potato (cultivar 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.

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:
energy :: sustainability :: ethanol :: biomass :: biofuels :: biohydrogen :: bioplastics :: starch :: sweet potatoes :: carbon dioxide ::

According to CO2 Science, the results mean that for sweet potato plants, as well as many other plants that have been similarly studied, 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.

Sweet potatoes are good starch producers and may yield some 40 to 50% more of it than corn, white potatoes and wheat. Per hectare, starch productivity can be 3 to 4 times higher than corn, and twice that of cassava. In short, sweet potatos are set to become important sources of industrial starch, needed to drive the bioeconomy. This carbon-neutral economy is aimed at replacing petroleum products, which contribute to climate change because of their carbon dioxide emissions.

References:
Teixeira da Silva, J.A., Giang, D.T.T. and Tanaka, M. 2005 "The Growth Response of Sweet Potato Plants to Very High Atmospheric CO2 Concentrations Reference. Microprogation of sweetpotato (Ipomoea batatas) in a novel CO2-enriched vessel." Journal of Plant Biotechnology 7: 67-74.

CO2 Science: The Growth Response of Sweet Potato Plants to Very High Atmospheric CO2 Concentrations - August 8, 2007.

Biopact: Japan's Cosmo Oil plans biofuel plants in Philippines - range of tropical feedstocks - June 13, 2007

Biopact: Sweet potatoes and the carbohydrate economy - January 07, 2007