Crop Nutrients Fall as CO2 Rises

greenhouse-growingAt the elevated levels of atmospheric CO2 anticipated by around 2050, crops that provide a large share of the global population with most of their dietary zinc and iron will have significantly reduced concentrations of those nutrients, according to a new study led by the Harvard School of Public Health published in Nature. Given that an estimated 2 billion people suffer from zinc and iron deficiencies, the reduction in these nutrients represents the most significant health threat ever shown to be associated with climate change.

Some previous studies of crops grown in greenhouses and chambers at elevated levels of CO2 revealed nutrient reductions, but those studies were criticized for using artificial growing conditions. Experiments using free air carbon dioxide enrichment (FACE) technology became the gold standard as FACE allows plants to be grown in open fields at elevated levels of CO2, but those prior studies had small sample sizes and have been inconclusive.

Researchers analyzed data involving 41 cultivars (genotypes) of grains and legumes from the C3 and C4 functional groups (plants that use C3 and C4 carbon fixation) from seven different FACE locations in Japan, Australia and the United States. The level of CO2 across all seven sites was in the range of 546-586 parts per million (ppm). They tested the nutrient concentrations of the edible portions of wheat and rice (C3 grains), maize and sorghum (C4 grains) and soybeans and field peas (C3 legumes).

The results showed a significant decrease in the concentrations of zinc, iron and protein in C3 grains. For example, zinc, iron and protein concentrations in wheat grains grown at the FACE sites were reduced by 9.3 percent, 5.1 percent and 6.3 percent respectively, compared with wheat grown at ambient CO2. Zinc and iron were also significantly reduced in legumes; protein was not.

This article appears in the July 2014 issue of Acres U.S.A.