A major study released last week indicates that rising atmospheric carbon dioxide (CO2) levels may reduce the nutrients available in some important food crops. This finding suggests that billions of people would be at greater risk of experiencing nutrient deficiencies as CO2 levels rise.
The international research project was led by Samuel S. Meyers of Harvard University. Researchers worked on seven experimental plots in Australia, Japan and the United States. Six crops – corn, field peas, rice, sorghum, soybeans and wheat – were raised under natural conditions, but with the carbon dioxide level raised to between 546 and 586 parts per million.
The current CO2 concentration is around 400 ppm, well above the pre-industrial world average of about 280 ppm.
The researchers studied 41 cultivars (genotypes) of plants that use different methods for extracting carbon dioxide from the atmosphere. Most of the crops being studied used C3 carbon fixation, sorghum using C4. Zinc, protein and iron concentrations all went down at the elevated CO2 levels used in this study. However, C4 crops like sorghum seem to be less affected by higher CO2 levels.
There are three types of photosynthesis – C3, C4 and crassulacean acid metabolism (CAM). The whole leaf carries out photosynthesis in a C3 plant. With C4 photosynthesis structures inside the plant’s cells carry out photosynthesis. Those plants are able to store carbon dioxide in their cells, so they might be less sensitive to rising carbon dioxide levels.
Wheat, soybeans, rice and peas exposed to such a high level of carbon dioxide all had less zinc and iron. Wheat, rice and peas had less protein as well. The major micronutrient deficiencies worldwide are in iron, vitamin A and zinc, Myers said. He also said he was unaware of any efforts to study how elevated carbon dioxide would affect vitamin A. Still, the research shows that as carbon dioxide increases the nutrient value of some staple food crops may decline.
Extreme weather and rising temperatures are not the only threats to crops. A higher carbon dioxide concentration, similar to that expected to happen by 2050, is connected with a decrease in two key crop nutrients – iron and zinc. Around two billion people worldwide already have deficiencies in one of those nutrients.
The mechanism by which carbon dioxide concentrations affect nutrient levels is not clear. The decline is worrisome because billions of people rely on rice, peas, soybeans and wheat for most of their dietary iron and zinc.
Efforts are underway to grow biofortified crops, plants deliberately bred to increase their nutritional value, and create new cultivars that are less sensitive to elevated CO2. Those breeding programs are not a cure-all, Myers said, because the cost of the new seeds and many other criteria determine what farmers will actually buy.
The simplistic view of climate change being good for agriculture ignores the fact that rising CO2 levels cause a number of problems. A potential loss of nutrients is only one. Carbon dioxide has been shown to reduce yields of some crops. Even if a warmer climate opens up new areas for agriculture there is no guarantee those areas will have good soil and adequate water. Climate change may help spread crop diseases like coffee rust.
As the world’s population grows and carbon dioxide increases, the news that carbon dioxide may cut nutrients in food crops is causing concern. Loss of nutrients in some of the planet’s staple food crops is only one of the developing issues.
By Chester Davis