Cassava about‐FACE: Greater than expected yield stimulation of cassava (Manihot esculenta) by future CO₂ levels

Abstract

Globally, cassava is the second most important root crop after potatoes and the fifth most important crop overall in terms of human caloric intake. In addition to its growing global importance for feed, fuel, and starch, cassava has long been vital to food security in Sub-Saharan Africa. Climate change is expected to have its most severe impact on crops in food insecure regions, yet little is known about how cassava productivity will respond to climate change. The most important driver of climate change is globally increasing atmospheric CO 2 concentration ([CO 2 ]). However, the potential for cassava to enhance food security in an elevated [CO 2 ] world is uncertain as greenhouse and open top chamber (OTC) study reports are ambiguous. Studies have yielded misleading results in the past regarding the effect of elevated [CO 2 ] on crop productivity, particularly in cases where pots restricted sink growth. To resolve these conflicting results, we compare the response of cassava to growth at ambient (ca. 385 ppm) and elevated [CO 2 ] (585 ppm) under field conditions and fully open air [CO 2 ] elevation. After three and half months of growth at elevated [CO 2 ], above ground biomass was 30% greater and cassava root tuber dry mass increased over 100% (fresh weight increased 89%). High photosynthetic rates and photosynthetic stimulation by elevated [CO 2 ], larger canopies, and a large sink capacity all contributed to cassava's growth and yield stimulation. Cassava exhibited photosynthetic acclimation via decreased Rubisco capacity early in the season prior to root tuber initiation when sink capacity was smaller. Importantly, and in contrast to a greenhouse study, we found no evidence of increased leaf N or total cyanide concentration in elevated [CO 2 ]. All of our results are consistent with theoretical expectations; however, the magnitude of the yield increase reported here surpasses all other C 3 crops and thus exceeds expectations.

Effects of elevated CO2 concentration on growth and photosynthesis of Chinese yam under different temperature regimes

“…In these studies, increased [CO 2 ] has been reported to lead to increased dry matter production in many major food crops, including rice (Baker et al, 1992;Cheng et al, 2009;Roy et al, 2012;Shimono et al, 2008;Ziska et al, 1997), potato (Aien et al, 2014;Chen & Setter, 2012;Conn & Cochran, 2006;Miglietta et al, 1998), and cassava (Cruz et al, 2014;Imai et al, 1984;Rosenthal et al, 2012). To the best of our knowledge, however, no reports have appeared on yam response to elevated [CO 2 ].…”

Climate Change and Potato Production in Contrasting South African Agro-ecosystems 1. Effects on Land and Water Use Efficiencies

“…Firstly, Fleisher et al (2008) observed that potato plants grown under elevated CO 2 levels had consistently higher photosynthetic rates through most of the growing season and that this extra assimilate was mostly partitioned to the tubers, resulting in higher dry matter production and harvest indices, and therefore higher tuber yields. Rosenthal et al (2012) found a very strong positive yield response to elevated CO 2 levels in cassava (89% increase), another C3 crop with belowground storage organs. They also ascribed the strong positive response of root and tuber crops to the fact that storage organs are formed early in the growing season, and these act as effective sinks for carbohydrates throughout most of the growing season.…”

The Influence of Climate Change on Global Crop Productivity

“…An important distinction for CO 2 sensitivity is between C4 grains (least responsive), C3 grains (more responsive), and root and tuber crops (most responsive). For example, a recent field study of cassava showed roughly a doubling of dry mass for a CO 2 increase from 385 to 585 mL L 21 (Rosenthal et al, 2012).…”