Rice, is a staple food in many developing countries and this important human dietary content is fast losing its nutritional value due to human activities which impact negatively on the climate according to a new study published in Science Advances.
After wheat, rice is the second most important food crop in the developing world. Over two billion people in Asia and hundreds of millions in Africa and Latin America depend on rice for their daily calorie needs. It’s estimated that more than 40,000 varieties of cultivated rice (the grass species Oryza sativa) exist.
Rice is also an important source of protein and vitamins, which is why the latest findings by researchers at the University of Tokyo are so worrisome. Their experiments suggest that rising CO2 levels in the atmosphere are lowing the nutritional value of rice, specifically iron, zinc, protein, and vitamins B1, B2, B5, and B9.
The team grew rice at sites in China and Japan using an open-field method called FACE (free-air CO2 enrichment). Professor Kazuhiko Kobayashi and colleagues at the University of Tokyo decided to grow the rice in an open field because plants raised in a closed greenhouse do not grow as they would in normal field conditions. Air with higher carbon dioxide concentrations, as expected in the second half of this century (568 to 590 parts per million), was blown through 17-meter-wide (56-foot-wide) plastic pipe octagons at about 30 centimeters (1 foot) above the tops of plants within standard rice fields.
In total, the researchers analyzed 18 different varieties of rice for protein, iron, and zinc levels. Nine varieties of rice grown in China were used for the vitamin B1, B2, B5, and B9 analyses.
The two FACE experiments have provided a unique opportunity to investigate how a crop fares in response to predictably elevated levels of CO2 in the atmosphere. But like with any other unique science experiment, the Japanese researchers had to overcome some challenges, including the presence of uninvited guests such as raccoons and blood-sucking insects.
Little is known about the mechanisms responsible for the decline in nutrient concentrations associated with elevated CO2. Some authors have proposed “carbohydrate dilution” whereby CO2-stimulated carbohydrate production by plants dilutes the rest of the grain components, but studies so far have been inconclusive. What’s certain is that it’s happening.
Zinc deficiency is already linked to around 800,000 deaths among under-fives, in whom it can seriously exacerbate such conditions as diarrhea, pneumonia, and malaria, while iron deficiency is the main cause of anemia, a condition that contributes to around one in every five maternal deaths around the world.
As the world’s population continues to swell, not only will developing countries have to grow more rice and improve their yield, they will also have to find ways to offset the poorer nutritional value of the crops. Of course, rice won’t be alone. Previous studies have found that rising levels of carbon dioxide in the atmosphere reduce the nutritional value of other staple crops, such as wheat or soy.
“This is one of the multitudes of challenges of climate change due to the energy production based on fossil fuel burning. We, in the so-called developed countries, take advantage of the fossil fuel energies, while having little troubles with the less nutritious grains, because we take the nutrients from other foodstuffs. On the other hand, those in the less-developed countries depend grains for their nutrient intake and would be affected by the changes in grain nutrient content. And, they are much less responsible for the climate change than we are on per person basis. This is really a shame on us, I think,” Kobayashi concluded.
