Rising carbon dioxide level in the atmosphere is lowering protein in key dietary crops which may affect the nutritious value of foods, a new study has warned.
For the first time, a field test has demonstrated that elevated levels of carbon dioxide inhibit plants' assimilation of nitrate into proteins, indicating that the nutritional quality of food crops is at risk as climate change intensifies, researchers said.
"Food quality is declining under the rising levels of atmospheric carbon dioxide that we are experiencing," said lead author Arnold Bloom, a professor in the Department of Plant Sciences at University of California - Davis.
"Several explanations for this decline have been put forward, but this is the first study to demonstrate that elevated carbon dioxide inhibits the conversion of nitrate into protein in a field-grown crop," he said.
The assimilation, or processing, of nitrogen plays a key role in the plant's growth and productivity.
In food crops, it is especially important because plants use nitrogen to produce the proteins that are vital for human nutrition. Wheat, in particular, provides nearly one-fourth of all protein in the global human diet.
To observe the response of wheat to different levels of atmospheric carbon dioxide, the researchers examined samples of wheat that had been grown in 1996 and 1997 in the Maricopa Agricultural Center near Phoenix, Arizona.
At that time, carbon dioxide-enriched air was released in the fields, creating an elevated level of atmospheric carbon at the test plots, similar to what is now expected to be present in the next few decades.
Control plantings of wheat were also grown in the ambient, untreated level of carbon dioxide.
In the recent study, the researchers documented that three different measures of nitrate assimilation affirmed that the elevated level of atmospheric carbon dioxide had inhibited nitrate assimilation into protein in the field-grown wheat.
"These field results are consistent with findings from previous laboratory studies, which showed that there are several physiological mechanisms responsible for carbon dioxide's inhibition of nitrate assimilation in leaves," Bloom said.
Bloom noted that other studies also have shown that protein concentrations in the grain of wheat, rice and barley - as well as in potato tubers - decline, on average, by approximately 8 per cent under elevated levels of atmospheric carbon dioxide.
"When this decline is factored into the respective portion of dietary protein that humans derive from these various crops, it becomes clear that the overall amount of protein available for human consumption may drop by about 3 per cent as atmospheric carbon dioxide reaches the levels anticipated to occur during the next few decades," Bloom said.
The finding was published in the journal Nature Climate Change.
