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Cassava plants will thrive as CO2 levels rise

Scientists at the University of Illinois  have discovered that the root crop cassava, which feeds more than a billion people, will thrive under the atmospheric conditions projected for the second half of this century. 

As carbon dioxide levels continue to rise rapidly in the atmosphere, plants have more CO2 available for photosynthesis and development. Experts have been working to understand how higher CO2 levels will affect crop yields and whether crops will retain their nutritional value. 

In collaboration with scientists at Monash University, the team grew cassava in an outdoor research facility called SoyFACE. This facility was designed to artificially boost carbon dioxide so that researchers can study how crops will respond to higher atmospheric concentrations of CO2 in the coming decades.

The researchers discovered that elevated CO2 levels boosted the crop yields of seven out of eight types of cassava by between 22 and 39 percent. Each strain selected for the study is preferred by farmers in Africa, where cassava makes up a quarter or more of diets in several countries. 

Unlike previous investigations into the effects of rising CO2 on other crops, the team found no decrease in protein quality or nitrogen content in the leaves, which are consumed by humans and livestock in addition to the starchy tubers.

“We wanted to know how cassava copes with elevated carbon dioxide,” said study co-author Professor Donald Ort. “Sometimes, plants cannot make use of extra carbohydrates, which then triggers the plant to down-regulate photosynthesis. We found cassava could maintain photosynthetic efficiency and nutritional quality.”

Plants use tiny pores in their leaves called stomata to take in carbon dioxide. At the same time, they lose water from these pores. The study showed that when carbon dioxide levels increase from 400 to 600 ppm, cassava leaves could conserve 58 percent more water on average by optimizing the rate that carbon enters compared to water exiting the leaf.

“Cassava’s natural ability to produce high yields with little water is part of what makes this crop a staple in drought-prone regions across sub-Saharan Africa,” said study co-author Amanda De Souza. “It is not surprising to see this trait magnified in C3 crops, but it is encouraging since we predict water scarcity to be a major barrier to food security.”

There did not appear to be a significant difference in how well the eight cassava varieties photosynthesized, but the team did observe changes in their growth and development due to how the plants distributed carbohydrates to their roots, stems, and leaves. 

“We can capitalize on these differences in partitioning to develop cassava varieties that sink more carbon into their roots to boost yields,” said study lead author Ursula Ruiz Vera. “We aim to enhance the natural resilience and productivity of this crop that is uniquely situated to help smallholder farmers withstand pressures from our changing climate.”

The research is the result of a partnership between two international research projects that are supported by the Bill & Melinda Gates Foundation. 

The study is published in the Journal of Experimental Botany.

By Chrissy Sexton, Staff Writer

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