Rising emissions may double sweet potato size

Sweet potato tubers can almost double in size in carbon dioxide-rich conditions, research has found

Forest & Kim Starr

[LIMA] Rising levels of carbon dioxide (CO₂) in the atmosphere caused by human-driven emissions might lead to larger sweet potatoes, a staple food for many African and Asian countries, research reveals.

Sweet potatoes could double in size with the increase in CO₂ levels currently forecasted for the end of this century, according to research by a team from the University of Hawaii, United States. The team  presented their finding at a meeting of the American Geophysical Union, in San Francisco this month (3-7 December).

The researchers grew a white-fleshed sweet potato variety from Hawaii in two types of fertiliser at current CO₂ levels of 352 parts per million (ppm), as well as in three raised CO₂ environments: 763, 1,108 and 1,515 ppm.

According to the Intergovernmental Panel on Climate Change, atmospheric CO₂ levels will be between 500 and 1,000 ppm by the year 2100.

Even at 763 ppm of CO₂, the tubers grew up to 96 per cent larger.

"It is more than likely that we will be reaching much higher CO₂ levels than previously expected and it is therefore important to understand how plants will respond to elevated CO₂ at much higher concentrations," Ben Czeck, one of the researchers, tells SciDev.Net.

In addition, he says that climate change is expected to do the most harm to developing countries that rely heavily on root crops such as sweet potato.

The researchers now want to find out if growing larger sweet potatoes will have any negative impact on their nutritional content, Czeck says.

Previous studies revealed that the protein content in wheat, rice, barley and potatoes dropped by 15 per cent when grown under CO₂ levels double those of today. The drop is caused by a series of impacts on plant physiology stemming from the higher levels of the gas.

"The nutritional contents we are looking at are calories, dietary fibre, protein, sugars and micro- and macro-minerals," Czeck says.

Orange- and purple-fleshed varieties of sweet potato are rich in beta-carotene, which the body converts to vitamin A. They are being grown to try to reduce child malnutrition in African countries.

Gabriela Burgos, who leads the Quality and Nutrition Lab at the International Potato Center (CIP), in Peru, says it is vital to study how raised CO₂ levels will affect root and tuber crops, because much of the world's population depends on them for food.

"At CIP, we are trying to add more nutritional content to potato and sweet potato varieties, but if in a few years those varieties are going to be oversize, their nutritional content could be diluted," she tells SciDev.Net. So it is good to have some way of dealing with the anticipated changes, she adds.  

But Wolfang Gruneberg, CIP geneticist and sweet potato breeder, thinks the real problem will not be higher atmospheric CO₂ levels but the effect of raised temperatures on plants.

"Plants use water to cool down. There are many places in the tropical world with drought. So the problem is not going to be the carbon dioxide but the [extra] heat that it would generate," he says.

CIP is evaluating the temperature range that sweet potatoes can withstand. As part of this, Gruneberg is planting a number of sweet potato varieties from CIP's genebank — the most complete of the world — in the hottest areas in north Peru.

Link to the presentation poster [2.42MB]