12 January - 20 June 2016

Another blow from global warming - reduced food quality

9 Apr 14

A study by researchers at the University of California, Davis, demonstrates the detrimental effect of increased atmospheric carbon on the nutritional value of food crops. The study focused on wheat, and observed that the total protein and nitrogen concentrations in the crop declined with increased CO2 levels in the atmosphere. These levels are expected to increase this century with global warming, meaning that new fertiliser approaches may be required in order to combat the effect on foodstuffs.

The wheat samples tested were harvested nearly twenty years ago, and the leaf tissue preserved through oven drying then storing it in evacuated plastic bags. The significance of these particular samples is that the site in which they were grown had had CO2-enriched air released into it, enabling the atmospheric concentration to be controlled at 548μmol mol-1 - a broadly similar level to that expected to be reached within the next few decades under current trends. Control samples grown at ambient CO2 (363μmol mol-1) were also preserved.

The recent study took these samples and investigated the isotopic nitrogen composition of the nitrate present - a new analysis that was not available at the time the samples were grown. The reason for isotopic concentration being studied was that this data provides insight into nitrate assimilation into protein, and therefore the crop's nutritional value. It was found that for the crops grown in elevated CO2 conditions the proportion of nitrogen-15 compared to nitrogen-14 was less than for the crops grown in ambient CO2 conditions, suggesting that nitrogen-14-containing nitrate had been preferentially assimilated. This preferential assimilation is known to occur unless limited by nitrate availability, suggesting that nitrate was more available in the elevated CO2 crops, presumably as it was being assimilated more slowly. Two other measures of nitrate assimilation also supported this conclusion.

The outcome of this slower assimilation is reduced protein concentration in the wheat - and other studies have shown similar results for rice, barley and potato tubers. There are several reasons why nitrate assimilation is slower in plants grown in CO2-enriched atmospheres, due to the CO2's impact on various physiological mechanisms. According to the authors, the overall outcome is that the protein available for human consumption will decrease by an estimated 3% as atmospheric CO2 levels approach par with those in the artificially enriched environment of this experiment, unless more sophisticated approaches to nitrogen fertilisation are employed. [ScienceDaily]

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