Researchers discover that plant nutrients like zinc, iron and protein decrease as carbon dioxide levels increase.
RESEARCHERS have made the discovery that as carbon dioxide levels rise, some grains and legumes will become significantly less nutritious than they are today.
Eight institutions from Australia, Israel, Japan and the U.S. contributed to the research, reported in the journal Nature, which looked at multiple varieties of wheat, rice, field peas, soybeans, corn and sorghum grown in fields with atmospheric carbon dioxide levels like those expected in the middle of this century. (Atmospheric carbon dioxide concentrations are currently approaching 400 parts per million and are expected to rise to 550 ppm by 2050.)
The teams simulated high carbon dioxide levels in open-air fields using a system called Free Air Concentration Enrichment (FACE), which pumps out, monitors and adjusts ground-level atmospheric carbon dioxide to simulate future conditions. In this study, all other growing conditions — sunlight, soil, water and temperature — were the same for plants grown at high carbon dioxide levels and those used as controls.
The experiments revealed that the nutritional quality of a number of the world's most important crop plants dropped in response to elevated carbon dioxide.
The study contributed "more than 10-fold more data regarding both the zinc and iron content of the edible portions of crops grown under FACE conditions" than were available from previous studies, the team noted.
"When we take all of the FACE experiments we've got around the world, we see that an awfully lot of our key crops have lower concentrations of zinc and iron in them (at high carbon dioxide)," said University of Illinois plant biology and Institute for Genomic Biology professor Andrew Leakey, an author on the study. "Zinc and iron deficiency is a big global health problem already for at least 2 billion people."
Zinc and iron content decreased significantly in wheat, rice, field peas and soybeans. Wheat and rice also saw notable declines in protein content at higher carbon dioxide levels.
"Across a diverse set of environments in a number of countries, we see this decrease in quality," Leakey said.
Nutrients in sorghum and corn remained relatively stable at higher carbon dioxide levels because these crops use a type of photosynthesis, called C4, that already concentrates carbon dioxide in their leaves, Leakey explained.
"C4 is sort of a fuel-injected photosynthesis that maize, sorghum and millet have," he said. "Our previous work here at Illinois has shown that their photosynthesis rates are not stimulated by being at elevated carbon dioxide. They already have high carbon dioxide (levels) inside their leaves."
More research is needed to determine how crops grown in developing regions of the world will respond to higher levels of atmospheric carbon dioxide, Leakey said.
"It's important that we start to do these experiments in tropical climates with tropical soils, because that's just a terrible gap in our knowledge, given that that's where food security is already the biggest issue," he said.
The collaboration included researchers from Harvard University, which led the effort; Ben-Gurion University of the Negev in Beer Sheva, Israel; the University of Illinois; the University of California-Davis; the U.S. Department of Agriculture's Agricultural Research Service; the National Institute for Agro-Environmental Sciences in Ibaraki, Japan; the University of Melbourne in Australia; the University of Arizona; the University of Pennsylvania, and The Nature Conservancy.