Continued elevated carbon dioxide concentrations in the atmosphere may reduce forage quality among the world’s grasslands and lead to reduced weight gain in animals.

That’s according to a five-year Colorado study by USDA-ARS and Colorado State Univer-sity researchers.

Plant physiologist Jack Morgan, who led the study, points out that atmospheric concentrations of carbon dioxide have been rising steadily during the last 150 years. The compound is considered a major greenhouse gas because of its ability to trap heat near the Earth’s surface. Fossil-fuel burning, forest clearing and industrial manufacturing account for most of the increased carbon dioxide emissions.

The experiment was conducted on native shortgrass prairie in northern Colorado. The scientists used six open-top chambers, each with more than 25 plant species. But three peren-nial native grass species dominated each chamber.

Three of the chambers were infused with ambient air containing about 360 ppm carbon dioxide to mimic present atmospheric conditions. The other three chambers were infused with ambient air that had been injected with pure carbon dioxide to double the amount to 720 ppm.

The scientists found that forage quality declined in all three dominant grasses under the elevated carbon dioxide conditions, due largely to lower tissue nitrogen content. They also found that the least desirable of the three grasses (needle-and-thread grass), produced higher yields under elevated carbon dioxide, while yields of the two higher-quality grasses remained unchanged.