To study the effect of climate change on plant nutritional quality and yield, a team led by Ros Gleadow of Monash University tested cassava and sorghum under a series of scenarios. The species belong to a plant group that produces chemicals called cyanogenic glycosides, which break down to release poisonous cyanide gas if the leaves are crushed or chewed. About 10% of all plants and 60% of crop species produce such chemicals.

Gleadow's team grew cassava and sorghum at three different levels of carbon-dioxide (CO2) -- at about 360 parts per million (ppm) in the atmosphere, at about 550 ppm and at 710 ppm. Current levels are just under 390 ppm.

In cassava, Gleadow told Reuters, “what we found was the amount of cyanide relative to the amount of protein increases”. At double current CO2 levels, the toxin level was much higher, while protein levels fell. Humans and cattle need protein to break down the cyanide. However, a 50% or greater drop in the number of tubers caused the most concern, according to Gleadow. Although the levels of toxin in the tubers did not increase with CO2, she said, the tubers were fewer and smaller.

About 750 million people in Asia, Africa and Latin America currently rely on cassava as a staple. “If we're going to adapt in the future to a world with twice today's CO2,” Gleadow told Reuters, “we need to understand how plants are working, how they are responding and what cultivars we need to develop” over the next 20 to 30 years.

Similar results were found in the team's study of a type of sorghum fed to cattle in Australia and Africa.
 

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