Cassava can benefit from weather changes more than other crops

Carbon dioxide fuels photosynthesis, the process by which plants generate their food in the form of carbohydrates. Atmospheric carbon dioxide levels are rising rapidly, but there is uncertainty that plants can turn these extra resources into higher yields while maintaining nutritional quality.

A team from the University of Illinois and Monash University has studied how the cassava crop, which feeds over 1 billion people, will adapt to the expected amount of carbon dioxide by the second half of this century. They grew the crop in an outdoor research facility called SoyFACE that artificially raises carbon dioxide to understand how rising levels will impact crops over the next few decades.

This study is the result of a partnership between two international research projects supported by the Bill & Melinda Gates Foundation. Cassava Source-Sink focuses on improving cassava yield; Realizing Enhanced Photosynthetic Efficiency (RIPE) is improving photosynthesis to increase yields with support from the Gates Foundation, Foundation for Food and Agriculture Research and UK Foreign, Commonwealth & Development Office.

In Journal of Experimental Botany, reported significant increases in yield ranging from 22 to 39 percent in seven out of eight varieties of cassava. Each cultivar selected for the study is “farmers’ favorite” in Africa, where cassava makes up a quarter or more of diets in several countries. Contrary to previous studies on other crops, they found no decrease in protein quality or nitrogen content in the leaves, which are consumed by humans and livestock in addition to starchy tubers.

“We wanted to know how cassava copes with high carbon dioxide,” said RIPE deputy director Donald Ort, Robert Emerson Professor of crop science and plant biology at the Carl R. Woese Institute of Genomic Biology in Illinois. “Sometimes, plants cannot make use of extra carbohydrates, which then triggers the plant to down-regulate photosynthesis. We found that cassava could maintain photosynthetic efficiency and nutritional quality.”

To absorb carbon dioxide, plants open tiny pores in the leaves (called stomata) that allow water to escape through transpiration. This study found that when carbon dioxide levels increase from 400 to 600 ppm, cassava leaves could store on average 58% more water by optimizing stomatal conductance, which is the rate at which carbon enters relative to the water coming out of the leaf.

“Cassava’s natural ability to produce high yields with little water is part of what makes this crop a staple food in drought-prone regions of sub-Saharan Africa,” said co-author Amanda De Souza, postdoctoral researcher for the RIPE project in Illinois. “It is not surprising to see this trait amplified in C3 crops, but it is encouraging as we expect water scarcity to be a major barrier to food security.”

While the team didn’t find much of a difference in how well the eight varieties photosynthesize well, they found differences in their growth and development due to how the plants distributed carbohydrates to their roots, stems and leaves, called partitioning. Cassava plant growers try to maximize the resources allocated to the roots, called the “pit” where the plant stores the carbon.

“We can capitalize on these differences in partitioning to develop cassava varieties that absorb more carbon in their roots to increase yields,” said Ursula Ruiz Vera, a postdoctoral researcher for both projects, who led the study in Illinois. “Our goal is to improve the natural resilience and productivity of this crop which is uniquely positioned to help smallholder farmers withstand the pressures of our changing climate.”