Nutritional Value of Rice Decreases With Increased Levels of Atmospheric Carbon Dioxide

Increasing levels of atmospheric carbon dioxide due to rising air pollution levels can reduce the nutritional value of rice according to an international research team that studied rice samples obtained from field experiments undertaken by a professor in the University of Tokyo. "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 Professor Kazuhiko Kobayashi of the University of Tokyo, co-author of the recent study and expert in effects of air pollution on agriculture.

Details of Study

The team grew rice under experimentally created high carbon dioxide concentrations and analyzed the samples for their nutritional content. The details of the study is as follows:

• The rice was cultivated at research sites in China and Japan using an open-field method where the scientists built 17-meter-wide (56-foot-wide) plastic pipe octagons raised about 30 centimeters (1 foot) above the top of the crops in standard rice fields.
• A network of sensors and monitors estimated wind speed and direction to find out how much carbon dioxide comes out of the pipes in order to increase the local carbon dioxide concentration to the desired test level. The technique is termed as Free-Air Carbon dioxide Enrichment (FACE)

"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. 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," said Kobayashi.

• The pipes and tubes had to be raised above ground level to prevent wildlife such as raccoons from chewing through the crops and disrupting the experiment.
• The scientists assessed a total of 18 different varieties of rice for protein, iron, and zinc content. Nine varieties of Chinese rice were tested for the vitamin B1, B2, B5, and B9 levels. The medical terms for the vitamins are thiamine (B1), riboflavin (B2), pantothenic acid (B5), and folate (B9).
• The levels of key minerals and vitamins were reduced in rice grown under high CO2 levels. Specifically, concentrations of vitamins B1, B2, B5, and B9, iron, protein and zinc were reduced in rice grown under high atmospheric CO2 levels that would be expected in the second half of this century (approximately 568 to 590 parts per million).
• Interestingly not all varieties of rice demonstrated the same degree of decline in nutritional quotient. Thus, future research projects could focus on production of rice varieties that retain their nutritional value despite increased carbon dioxide levels.

Thus, the findings of the study suggest that rising CO2 levels in the atmosphere that would be expected to occur in the next few decades could lower the nutritional value of rice and put entire populations at risk of malnutrition.

Statistics estimate that nearly six hundred million people in Bangladesh, Cambodia, Indonesia, Myanmar, Lao People's Democratic Republic, Vietnam, and Madagascar derive at least 50 percent of their daily calories and/or protein directly from rice. This was also true in Japan during the 1960s, however, current Japanese receive only about 20 percent of their daily energy requirements from rice.

Takeaway from Study

The findings of the study underscore the importance of initiating urgent measures to produce rice varieties that manage to retain their nutritional value despite exposure to high atmospheric carbon dioxide.

This is especially important since rice is a low cost staple diet of several populations in developing countries and are at risk of malnutrition if the nutritional value of low-cost staple foods like rice goes down.

References:

1. Chris Mooney, "Rice, the staple food of billions, could become less nutritious because of climate change" (2018), journal Science Advances
2. Carbon dioxide in Earth's atmosphere - (https://en.wikipedia.org/wiki/Carbon_dioxide_in_Earth%27s_atmosphere)

Source-Medindia