An optimistic future of C crop broomcorn millet ( L.) for food security under increasing atmospheric CO concentrations.

Broomcorn millet, a C cereal, has better tolerance to environmental stresses. Although elevated atmospheric CO concentration has led to grain nutrition reduction in most staple crops, studies evaluating its effects on broomcorn millet are still scarce. The yield, nutritional quality and metabolites of broomcorn millet were investigated under ambient CO (CO, 400 µmol mol) and elevated CO (CO, CO+ 200 µmol mol) for three years using open-top chambers (OTC). The results showed that the yield of broomcorn millet was markedly increased under CO compared with CO. On average, CO significantly increased the concentration of Mg (27.3%), Mn (14.6%), and B (21.2%) over three years, whereas it did not affect the concentration of P, K, Fe, Ca, Cu or Zn. Protein content was significantly decreased, whereas starch and oil concentrations were not changed by CO. With the greater increase in grain yield, CO induced increase in the grain accumulations of P (23.87%), K (29.5%), Mn (40.08%), Ca (22.58%), Mg (51.31%), Zn (40.95%), B (48.54%), starch (16.96%) and oil (28.37%) on average for three years. Flavonoids such as kaempferol, apigenin, eriodictyol, luteolin, and chrysoeriol were accumulated under CO. The reduction in L-glutamine and L-lysine metabolites, which were the most representative amino acid in grain proteins, led to a reduction of protein concentration under CO. Broomcorn millet has more desirable nutritional traits for combating hidden hunger. This may potentially be useful for breeding more nutritious plants in the era of climate change.