Scientists are warning that rice, one of the world’s most important cereal crops and the primary food source for more than 2 billion people may become “less nutritious in the future.’’

Researchers in Japan and China have found that protein, iron and zinc levels in rice all fell significantly when grown in higher carbon dioxide environments.

For the experiments, scientists built 17-metre-wide octagons in Japanese and Chinese rice paddies that pumped carbon dioxide to simulate the kind of CO2 concentrations expected in the next 50 years (568-590 parts per million).

The research, published in the journal Science Advances, found on average from the varieties tested, protein levels fell by 10 per cent, zinc 8 per cent and iron 5 per cent.

Levels of vitamins B1, B2, B5, and B9 also fell though results were far more varied.

“When we looked at vitamin B we looked at nine different varieties from Japan and China and they interestingly responded to high CO2 concentration in different ways,” the University of Tokyo’s Kazuhiko Kobayashi said.

“Some varieties showed a very large decline, some varieties much less a drop of vitamin contents.”

Researchers are warning the nutritional changes could have significant health implications especially in poorer countries.

“For some populations in the world, rice is a major source of protein and also vitamins and also some other minerals,” Professor Kobayashi said.

“For those people, this is not very good news.”

Director of the ARC’s Centre of Excellence for Translational Photosynthesis, Professor Bob Furbank, said in theory higher CO2 levels were a good thing for growth but the reality proved somewhat different.

“On one hand we have the view that there will be a fertilising effect of having the extra carbon dioxide that’s available for photosynthesis that’s certainly the case,” he said.

“But there’s also the negative effects of climate change in terms of more frequent drought [and] higher temperatures, which can tend to negate the positive benefit of extra carbon dioxide from a photosynthetic perspective.

“This paper draws on the data they’ve produced to show there’s a detrimental effect on the quality of the rice grain in high CO2.”

Professor Furbank based at the Australian National University said researchers should now study and breed varieties that will yield quality not just quantity in high CO2 environments.

“I think it’s crucial and the work we do in [our Centre of Excellence] is more around improving yields — so we’re looking more at how to boost the amount of food available to the global population,” he said.

“But the nutritive quality of that food is equally as important.”

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