The nutritional deficiencies (Myers et al 2014 Nature) in zinc and iron constitute a major global public health problem. It is estimated that two billion people suffer from these deficiencies. Most of these people depend on grains and legumes as their main food source of zinc and iron.

Studies show that cereals (C3) and legumes have lower concentrations of zinc and iron when grown under conditions where the CO2 concentration is higher (and consistent with that expected in 2050). C3 plants, other than legumes, also have lower protein concentrations, while C4 crops appear to be less affected.

Figure: Effect of the increase in atmospheric CO2 concentration (CO2 = 689 ppm) on the concentration of C3 plants in minerals - review of FACE experiments (Loladze, 2014)

Little is known about the mechanisms at work to explain these decreases in protein, iron and zinc. Two hypotheses are currently being studied:

• The effect of CO2 enrichment on the mechanisms of mineral nutrition of plants (and in particular the assimilation of nitrates)
• The effect of CO2 enrichment on the decrease in the bioavailability of minerals in the soil

Figure: Competition between plants and soil microorganisms for absorption of minerals