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Carbon Dioxide and Cassava: Feeding the World's Undernourished
Volume 15, Number 49: 5 December 2012

In an extremely important paper published in Global Change Biology, Rosenthal et al. (2012) write that "given the projections that future food production will need to double to meet the global demand by 2050 (Lobell et al., 2008; Godfray et al., 2010; Tilman et al., 2011), there is an urgent need to assess the impact of climate drivers on crops of food insecure regions," noting in this regard that "more than 900 million people are undernourished and nearly 90% live in Sub-Saharan Africa, Asia, and the Pacific," citing the United Nations Food and Agriculture Organization (FAO, 2010).

Further to the point of their paper, the eight researchers write that "in Sub-Saharan Africa, the starchy root tuber crop cassava accounts for almost two-thirds of the direct human caloric intake," and that in areas where drought is recurrent, "cassava is harvested when other crops fail (FAO, 2005)," adding that cassava "provides food security during armed conflicts when above-ground crops are destroyed, as the cassava tuber remains viable below ground for up to three years (Cock, 1982; Lebot, 2009)."

So what can the rising atmospheric CO2 concentration do to enhance the multiple important roles played by cassava in combating global food insecurity, especially where the situation is most tenuous?

Somewhat ominously, Rosenthal et al. report that a recent greenhouse study on cassava found decreased yields at elevated CO2, and that the smaller yields were accompanied by increases in leaf, but not tuber, cyanide content (Gleadow et al., 2009), which finding was alarming to them because, as they write, "cassava leaves are eaten for their protein, and a higher leaf cyanide content suggests increased toxicity at elevated CO2." But since this study was conducted in a greenhouse, they opted to conduct a study to determine whether increases in cassava biomass or leaf toxicity would occur in plants grown under natural field conditions, employing free-air CO2 enrichment (FACE) technology.

This study was conducted at the SoyFACE facility located at the Experimental Research Station of the University of Illinois in Urbana-Champaign, where the air of four plots was enriched with CO2 to approximately 200 ppm above what was measured in four ambient-treatment plots. And what did the U.S. and Australian researchers learn?

Rosenthal et al. report that after three and a half months of growth at elevated CO2, the above-ground biomass of cassava was 30% greater, while cassava tuber dry mass was over 100% greater than it was in plants grown in ambient air. This result, in their words, "surpasses all other C3 crops and thus exceeds expectations." And they add that in contrast to the greenhouse study they cited, they found "no evidence" of increased leaf or total cyanide concentrations in the plants grown in the elevated CO2 plots. Thus, it would appear that the ongoing rise in the air's CO2 content will likely play a major positive role in helping to provide the doubled global food needs of mankind that will prevail at the turn of the century, which is but a mere 38 years from now.

Sherwood, Keith and Craig Idso

Cock, J.H. 1982. Cassava - a basic energy source in the tropics. Science 218: 755-762.

FAO. 2005. A Review of Cassava in Africa. Preface. Proceedings on the Validation Forum on the Global Cassava Development Strategy. International Fund for Agricultural Development and the Food and Agriculture Organization. Rome, Italy.

FAO. 2010. The State of Food Insecurity in the World. Pp. 10-11. United Nations Food and Agriculture Organization. Rome, Italy.

Gleadow, R.M., Evans, J.R., Mccaffery, S. and Cavagnaro, T.R. 2009. Growth and nutritive value of cassava (Manihot esculenta Cranz.) are reduced when grown in elevated CO2. Plant Biology 11: 76-82.

Godfray, H.C.J., Beddington, J.R., Crute, I.R., Haddad, L., Lawrence, D., Muir, J.F., Pretty, J., Robinson, S., Thomas, S.M. and Toulmin, C. 2010. Food security: the challenge of feeding 9 billion people. Science 327: 812-818.

Lebot, V. 2009. Tropical Root and Tuber Crops: Cassava, Sweet Potato, Yams and Aroids. CABI, Oxfordshire, United Kingdom.

Lobell, D.B., Burke, M.B., Tebaldi, C., Mastrandrea, M.D., Falcon, W.P. and Naylor, R.L. 2008. Prioritizing climate change adaptation needs for food security in 2030. Science 319: 607-610.

Rosenthal, D.M., Slattery, R.A., Miller, R.E., Grennan, A.K., Cavagnaro, T.R., Fauquet, C.M., Gleadow, R.M. and Ort, D.R. 2012. Cassava about-FACE: Greater than expected yield stimulation of cassava (Manihot esculenta) by future CO2 levels. Global Change Biology 18: 2661-2675.

Tilman, D., Balzer, C., Hill, J. and Befort, B.L. 2011. Global food demand and the sustainable intensification of agriculture. Proceedings of the National Academy of Sciences USA 108: 20,260-20,264.