Paper Reviewed
Ingvordsen, C.H., Gislum, R., Jorgensen, J.R., Mikkelsen, T.N., Stockmarr, A. and Jorgensen, R.B. 2016. Grain protein concentration and harvestable protein under future climate conditions. A study of 108 spring barley accessions. Journal of Experimental Biology 67: 2151-2158.

Noting that "protein from cereal grains is a key component of food and feed," citing Young and Pellett (1994), and further noting that Friedman (1996) had rightly reported that "the nutritional value of a crop is dependent on both its quantity and the composition of the protein produced," Ingvordsen et al. (2016) go on to describe how they had cultivated a set of 108 spring barley (Hordeum vulgare L.) accessions under current and predicted future day/night atmospheric temperatures (9/12°C) and CO2 concentrations (385/700 ppm) at the site of their study, both singly and in combination with each other, which experiment was conducted in a phytotron of the Technical University of Denmark, wherein they grew eight plants of each accession in 11-liter pots filled with 4 kg of sphagnum substrate and 10 g of NPK fertilizer (21-3-10) that were applied at sowing. And what did these efforts reveal?

The six Danish scientists report that (1) "across all genotypes, elevated CO2 slightly decreased protein concentration by 5%," but that (2) "elevated temperature substantially increased protein concentration by 29%," such that (3) "the combined treatment increased protein concentration across accessions by 8%." However, Ingvordsen et al. additionally report that (4) there was a "decrease in grain yield at combined elevated temperature and elevated CO2 that resulted in 23% less harvestable protein," which sounds pretty serious. But if one consults the Plant Growth Data section of our website, one will find that fully 40 prior studies of the effects of an approximate 300-ppm increase in the atmosphere's CO2 concentration resulted in a mean increase of 33.5% in ultimate barley production, which hugely-contrary finding suggests that the final word on the subject of elevated atmospheric CO2 concentrations and temperatures on protein production in barley plants has yet to be written.

References
Friedman, M. 1996. Nutritional value of proteins from different food sources. A review. Journal of Agricultural Food and Chemistry 44: 6-29.

Ingvordsen, C.H., Backes, G., Lyngkjaer, M.F., Peltonen-Sainio, P., Jensen, J.D., Jalli, M., Jahoor, A., Rasmussen, M., Mikkelsen, T.N., Stockmarr, A. and Jorgensen, R.B. 2015. Significant decrease in yield under future climate conditions: Stability and production of 138 spring barley accessions. European Journal of Agronomy 63: 105-113.

Young, V.R. and Pellett, P.L. 1994. Plant proteins in relation to human protein and amino acid nutrition. American Journal of Clinical Nutrition 59: 1203S-1212S.