May 25 (UPI) -- As carbon dioxide concentrations in Earth's atmosphere increase, the nutritional value of rice will decline, new research shows.
Researchers with the University of Tokyo tracked rice growth at experimental field sites across Japan and China. A system of pipes delivered different levels of CO2 to the rice plants. Wind sensors and gas detectors helped scientists ensure each plant was exposed to the correct amount of CO2.
Scientists analyzed rice samples from the experimental plants, measuring the amounts of iron, zinc, protein, and vitamins B1, B2, B5, and B9 found in each.
Their data revealed an inverse relationship between CO2 levels and nutritional qualities -- the higher the CO2 level, the lower the levels of vitamins and minerals. Researchers published the findings this week in the journal Science Advances.
"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," Kazuhiko Kobayashi, a professor at the University of Tokyo, said in a news release.
Kobayashi has been experimenting with his open-air, above-ground gas delivery system for nearly two decades, improving it along the way.
"I first started using this technique in 1998, because we knew that plants raised in a plastic or glass house do not grow the same as plants in normal, open field conditions," Kobayashi said. "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 century."
Today, Japanese eaters get just 20 percent of their daily food energy from rice, but elsewhere in Asia it remains as much a staple as it ever was. In Bangladesh, Cambodia, Indonesia, Lao People's Democratic Republic, Myanmar, Vietnam and Madagascar, some 600 million people rely on rice for 50 percent of their daily energy and protein intake.
Earlier this year, NOAA scientists announced the month of April averaged global CO2 concentrations above 410 parts per million, a new record.
To ensure rice-eaters can continue to get sufficient nutrients as the climate changes, scientists and farmers need to develop rice varieties with more resilient nutritional qualities.