By Cliff Montgomery – July 1st, 2009
Cassava is a plant first grown in the tropics of the Americas. Millions around the world now depend on its starchy root as a basic food source, as the hardy plant can grow in poor soil and withstand considerable drought. Currently cassava may only be eaten after it is properly dried to remove cyanide.
But such food staples will become more toxic and bring forth much smaller yields on a earth suffering from an overabundance of carbon dioxide (CO2) and drought, Australian scientists have determined.
The findings were presented on Jun 29th at a conference held in Glasgow, Scotland. Such facts underscore the need to produce staple foods which are more resistant to global warming, Ros Gleadow of Monash University in Melbourne told Reuters.
Gleadow and her team grew cassava and sorghum–a grass of the Old World often cultivated as a grain or forage, and used as a source for syrup–in a number of global warming scenario experiments. The team’s tests placed a special emphasis on CO2 levels, to better understand the effect on the plants’ nutritional qualities and yield.
The two species belong to a plant group which produces cyanogenic glycoside chemicals. If the plants are chewed or crushed without first undergoing the proper preparation, the chemicals dissolve to release a poisonous cyanide gas.
Around 60 percent of modern crop species–and about 10 percent of all trees, herbs, vines and shrubs–produce dangerous cyanogenic glycosides.
Gleadow’s team grew both sorghum and cassava at three different CO2 levels:
1.) Just below the modern level of around 360 Parts Per Million in the atmosphere (PPM)
2.) At around 550 PPM
3.) And at almost double the modern level, or 710 PPM.
Current CO2 levels are barely under 390 PPM–about the greatest level of CO2 in the atmosphere in 800,000 years. About one-third of this carbon dioxide has been created since the beginning of the Industrial Revolution.
“What we found was the amount of cyanide relative to the amount of protein increases [in cassava during climate change],” Gleadow told Reuters.
At twice the current CO2 levels, toxin levels became much higher as protein levels fell. Thus anyone relying on cassava as a food source–especially during drought–will be at great risk of cyanide poisoning, according to the study.
While processing techniques may be used to reduce toxin levels in cassava leaves, higher CO2 levels also produced at least a 50 percent drop in the fleshy cassava stems, according to group findings.
Around 750 million individuals in Africa, Latin America and Asia depend on cassava for basic nourishment. The plant’s starchy tubers grow well even in dry regions, and they often are used to make essential foodstuffs like flour.
There was a ray of good news from the study: Toxin levels in the cassava root didn’t increase with carbon dioxide growth, as was the case with its edible leaves.
“[But] the downside…is that we found the plant didn’t grow nearly as well,” Gleadow told Reuters.
“There’s been this common assumption that plants will always grow better in a high CO2 world. And we’ve now found that these plants grew much worse and had smaller tubers,” she added.
Gleadow said that humans currently have a small time frame to find at least a partial solution to this food problem.
“We’ve got 20 to 30 years to develop cultivars, which is going to be absolutely essential because by then about 1 billion people will probably be reliant on cassava,” said Gleadow.
The group also studied a form of sorghum often fed to cows in Africa and Australia. Gleadow’s team discovered that the sorghum’s toxicity actually lessened at the greatest CO2 level. But the toxin levels of its leaves rose when the plant was placed in drought conditions.
“If we’re going to adapt in the future to a world with twice today’s CO2 we need to understand how plants are working, how they are responding and what cultivars we need to develop,” Gleadow told Reuters.
