Climate change is hitting home -- in the food pantry, this time here in Sacramento. Meanwhile, in Kansas, researchers there are attempting to reverse what they consider to be a critical mistake our ancestors made some 10,000 years ago - the planting of annual crops instead of perennials. They want to replace standard wheat with wheatgrass. See, "New Wheat Crop in the Works - WTVY." But here in Sacramento and Davis, a new field study, "Nitrate assimilation is inhibited by elevated CO2 in field-grown wheat," of wheat demonstrates how the nutritional quality of food crops can be diminished when elevated levels of atmospheric carbon dioxide interfere with a plant's ability to process nitrate into proteins. Findings from this wheat field-test study, led by a University of California - Davis plant scientist is published online since April 6, 2014, in the journal Nature Climate Change.
Food quality researchers from the University of California, Davis, say this new field study shows why food quality will suffer with rising CO2 levels. 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.
"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, according to the April 6, 2014 news release, Field study shows why food quality will suffer with rising CO2. "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 in the news release.
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.
Many previous laboratory studies had demonstrated that elevated levels of atmospheric carbon dioxide inhibited nitrate assimilation in the leaves of grain and non-legume plants. However there had been no verification of this relationship in field-grown plants.
Wheat field study
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, Ariz.
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.
Leaf material harvested from the various wheat tests plots was immediately placed on ice, and then was oven dried and stored in vacuum-sealed containers to minimize changes over time in various nitrogen compounds
A fast-forward through more than a decade found Bloom and the current research team able to conduct chemical analyses that were not available at the time the experimental wheat plants were harvested.
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, according to the news release.
3 percent protein decline expected
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 percent 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 percent as atmospheric carbon dioxide reaches the levels anticipated to occur during the next few decades," Bloom said, according to the news release.
While heavy nitrogen fertilization could partially compensate for this decline in food quality, it would also have negative consequences including higher costs, more nitrate leaching into groundwater and increased emissions of the greenhouse gas nitrous oxide, he explained. What do you think is happening to the quality of wheat? Now, that's a topic to explore regarding various possible causes of the decline in food quality as revealed in recent research studies. Comparing the data is a valuable research topic in itself.
In addition to Bloom, the research team on this study included Martin Burger, currently in UC Davis' Department of Land, Air and Water Resources; and Bruce A. Kimball and Paul J. Pinter, both of the U.S. Department of Agriculture's U.S. Arid-Land Agricultural Research Center in Maricopa, Arizona. Funding for the study was provided by the National Science Foundation and the National Research Initiative competitive grants program of the U.S. Department of Agriculture's National Institute of Food and Agriculture.