updated 12/29/2006 2:25:41 PM ET 2006-12-29T19:25:41

Researchers studying plants and trees near Yellowstone National Park's thermal vents hope to glean an indication of how rising carbon dioxide emissions could affect vegetation worldwide a century from now. Plants near the vents are exposed to nearly twice as much carbon dioxide as is normal.

But if carbon dioxide emissions from power plants and cars keep increasing at current rates, the amount of carbon dioxide at the vents now will become the worldwide norm in 100 years.

University of Wyoming researchers Shikha Sharma and David Williams sampled leaves from lodgepole pines, Yellowstone's dominant tree species, and Dalmatian toadflax, an invasive species, to see how increased carbon levels affect their growth and metabolism.

"We have the opportunity to see how plants are growing across a range of CO2 concentrations around the vents," Williams said.

The scientists have been able to determine that plants and trees near the vents get about 30 percent of their carbon dioxide from the vents.

The researchers could draw that conclusion because atmospheric carbon dioxide contains a radioactive isotope, carbon 14, that isn't present in carbon dioxide from the vents. Plant samples collected farther from vents contained more carbon 14.

Leaves from plants near the vents, meanwhile, tended to contain less protein. Williams said that means they had less nutritional value for animals that eat those plants.

"If you see the same response in the forage species, that is going to have implications for how the large herbivores interact with the vegetation," Williams said. "They'll have to eat more to sustain themselves."

The plants nearer the vents also didn't use water as efficiently.

"What we're finding is that the plants photosynthesize less effectively in presence of high CO2, which is contrary to what other studies have shown," Williams said. "The little pores in their leaves are opening up more and likely losing more water."

But Sharma and Williams also think that increased CO2 would help some invasive plants like Dalmatian toadflax expand into ranges by out-competing native plants.

"We think it's going to help these weeds because they are very fast-growing," Williams said. "Other research has shown that fast-growing weeds respond positively to elevated levels of CO2."

Much remains to be learned, however. It's still unclear, for example, whether plants near the vents are using more carbon dioxide than plants in normal atmospheric conditions.

Sharma said researchers might also want to look at how increased carbon dioxide affects the other types of plants that animals eat, such as willows and grasses.

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