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.
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.
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 said.
|Contact: Patricia Bailey|
University of California - Davis