Paper Reviewed
De Souza, A.P., Cocuron, J.-C., Garcia, A.C., Alonso, A.P. and Buckeridge, M.S. 2015. Changes in Whole-Plant Metabolism during the Grain-Filling Stage in Sorghum Grown under Elevated CO2 and Drought. Plant Physiology 169: 1755-1765.

De Souza et al. (2015) grew sorghum plants (cv BRS 330) in 40-L pots placed within four open-top chambers as described by De Souza et al. (2008), which they maintained at atmospheric CO2 concentrations of either approximately 400 ppm or 800 ppm for 120 days, at the midpoint of which period (60 days after planting, DAP) they (1) subjected the plants to drought during the grain-filling stage, (2) made numerous types of measurements at 90 and 120 days after planting and, last of all, (3) assessed the biochemical composition and intracellular metabolites of each plant organ. And what did they thereby learn?

The five researchers report that "the biomass of grains, which corresponds to yield, did not change significantly between treatments." But they say that "even though there were no changes in yield, the protein content per mass in grains was higher at elevated CO2," reporting that at 120 DAP they found "averages of 5% and 8% of protein in grains under ambient and elevated CO2, respectively," which results represent an approximate 60% increase in the protein content of the CO2-enriched sorghum grains. Thus, it would appear that rising atmospheric CO2 may well improve the nutritional quality of sorghum.

Reference
De Souza, A.P., Gaspar, M., Da Silva, E.A., Ulian, E.C., Waclawovsky, A.J., Nishiyama, M.Y. Jr., Dos Santos, R.V., Teixeira, M.M., Souza, G.M. and Buckeridge, M.S. 2008. Elevated CO2 increases photosynthesis, biomass and productivity, and modifies gene expression in sugarcane. Plant Cell and Environment 31: 1116-1127.