Rise in CO2 level makes rice less nutritious

Increased carbon dioxide levels in the atmosphere will reduce the nutritional value of rice, a study has found. In rice grown under higher carbon dioxide concentrations expected in the second half of this century — 568 to 590 parts per million —levels of iron, zinc, protein, and vitamins B1, B2, B5, and B9 were found to be reduced.

“Rice is not just a major source of calories, but also proteins and vitamins for many people in developing countries and for poorer communities within developed countries,” said Kazuhiko Kobayashi of the University of Tokyo.

Populations in countries with both the highest rice consumption and lowest gross domestic product may experience more malnutrition as the nutritional value of low-cost staple food like rice declines.

Not all varieties of rice responded in the same way, so future research projects may examine the possibility of finding varieties of rice that can remain nutritious despite the change in the atmosphere.

The rice was grown at research sites in China and Japan using an open-field method where researchers build 17-metre-wide plastic pipe octagons elevated about 30 centimeters above the tops of plants within standard rice fields.

A network of sensors and monitors measure wind speed and direction to determine how much carbon dioxide is released out of the pipes to raise the local carbon dioxide concentration to the desired experimental level. The technique is known as Free-Air Carbon dioxide Enrichment (FACE).

“This technique allows us to test the effects of higher carbon dioxide concentrations on plants growing in the same conditions that farmers really will grow them some decades later in this centur,” said Kobayashi.