Declining Iron and Zinc Content in Crops Due to Increasing Carbon Dioxide Concentrations in the Air

An estimated two billion people suffer from a deficiency of iron and zinc. How and if these micronutrient deficiencies can be compensated depends particularly on the iron and zinc content of the crops which are mainly consumed by the people affected. However, the usual micronutrient content in basic foodstuffs is endangered by a growing CO₂ burden in the atmosphere, warns an international team of scientists of Harvard University (1).

Experiments with wheat in Australia, with rice in Japan and with soybeans, peas and corn in the US have shown that the iron and zinc content can drop over 10% when crops grow at the predicted increased atmospheric CO₂ concentration for the middle of this century. Their protein content also decreases. How sensitive plants react to the CO₂ load, depends on the mechanism of their photosynthesis. While wheat, rice, and soybeans, like almost all other crops, slow down their photosynthesis at high temperatures, others, such as sorghum, have adapted better to the changed environmental conditions. Crops of the environmentally friendly C4-group[1] could maintain their nutrient content even under difficult growth conditions (2).

Foodnote
[1] C4 plants bind CO₂ better than C3 plants. They have adapted to warmer regions with higher light irradiation, as present in tropical and subtropical climates. Especially grasses and crops such as amaranth, millet, corn and sugarcane use C4 photosynthesis. See C4 plants.

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1. SS Myers et al. Increasing CO2 threatens human nutrition. Nature. 2014 Jun 5; 510(7503):139-42. doi: 10.1038/nature13179. Epub 2014 May 7. available https://www.ncbi.nlm.nih.gov/pubmed/24805231
2. ibidem, Fig 1 illustrates, how different crops have responded to the rising carbon dioxide content in the air: