A world with higher carbon dioxide levels and more periods of drought could lead to staple foods such as cassava becoming more toxic, according to Ros Gleadow from Monash University, Australia. She says that her findings stress the importance of developing climate-change-resistant cultivars to feed rapidly growing human populations.
Gleadow’s team tested cassava and sorghum under a variety of climate change scenarios, with a particular emphasis on CO2 levels, to study the effect on plant nutritional quality and yield. Both of these species contain cyanogenic glycosides, which break down to release toxic cyanide gas if leaves are crushed or chewed.
Three CO2 levels were tested: 360 ppm (the current CO2 level is about 390 ppm), 550 ppm and 710 ppm. With cassava, the scientists found a correlation between the amount of CO2, the amount of cyanide and the amount of protein. At double current CO2 levels, the level of toxin in the leaves was much higher while protein levels fell.
The ability of people and herbivores to break down the toxin mainly depends on eating enough protein, so that people who are dependent on cassava could be especially at risk of poisoning, particularly during drought. Cassava is a staple in parts of Africa, Latin America and Asia.
While it is technically possible to reduce the amount of CO2 in leaves during processing, the main drawback was a 50% reduction in the number of tubers – the main part of the plant used for food. The plant basically did not grow as well at high CO2 levels although, unlike the leaves, the toxin levels in the tuber were not affected by CO2.
At 550 ppm, the problem was not as serious, which means that scientists have 20-30 years to come up with climate-change-resistant cultivars.
Her team also looked at a type of sorghum commonly fed to cattle in Africa and Australia and found that it became less toxic at higher levels of CO2. However, leaf toxin levels rose under drought conditions.
Gleadow says her team is looking at creating mutations to get rid of the toxin response to drought.
A related study carried out by Stanford University researchers estimates that African growing seasons for the continent's staple foods – maize, millet and sorghum – will be hotter in nine out of 10 years by 2050. Another report by the White House forecasts that heat, floods, drought and pests would harm food yields and declared that cranberry production may no longer be possible by 2050 in its East Coast heartland.
If seed banks were improved, many African countries could switch to crop varieties already grown in hotter parts of the continent. But the Stanford study found that several nations in the Sahel will have to change food crops altogether, for example from maize to millet.
