Rising atmospheric CO2 and human nutrition: toward globally imbalanced plant stoichiometry?

Terrestrial vascular plants obtain their major constituent - carbon (C) - from atmospheric carbon dioxide (CO2), but draw all other chemical elements largely from the soil. Concentrations of these elements, however, do not change in unison with steadily increasing concentrations of CO2 [CO2]. Thus, relative to pre-industrial times, modern plants are experiencing a global elemental imbalance. Could this imbalance affect the elemental composition of plants, the most important food source on Earth? Apart from an overall decline in nitrogen concentration, very little is known about the effects of high [CO2] on other chemical elements, such as iron, iodine and zinc, which are already deficient in the diets of the half of human population. Here, I apply stoichiometric theory to argue that high [CO2], as a rule, should alter the elemental composition of plants, thus affecting the quality of human nutrition. The first compilation, to my knowledge, of published data supports the claim and shows an overall decline of the (essential elements):C ratio. Therefore, high [CO2] could intensify the already acute problem of micronutrient malnutrition.