Researchers use Yellowstone to explore effects of elevated CO2

Wyoming

Researchers in the University of Wyoming College of Agriculture are using radiocarbon signatures in carbon dioxide taken up by plants in Yellowstone National Park to show affects of long-term exposure to elevated levels of the greenhouse gas.

Photosynthetic responses of plants are then estimated from the stable carbon and oxygen isotope ratios in plant leaves, said Shikha Sharma, scientist and associate director of the UW Stable Isotope Facility in the college. Sharma is principal investigator and Professor David Williams is co-investigator in the project.

By comparing physiological responses across carbon dioxide concentration gradients near natural geologic sources of CO2 production in the Yellowstone caldera, researchers will be able to predict how increasing atmospheric CO2 concentrations will affect the photosynthetic productivity of the native lodgepole pine compared to the invasive weed species Dalmatian toadflax in the park.

Their aim is to study effects of increasing levels of CO2 on world vegetation.

"The large and rapid rise in atmospheric CO2 concentration due to human activity and associated global warming has the potential to alter Earth's climate system and affect terrestrial ecosystems," said Sharma. "An important source of uncertainty in predictions about atmospheric change is how plants will respond to increasing atmospheric CO2 and how climate changes interact with rising CO2 concentrations."

Much of the current research has been carried out in controlled environments, she said, or in short-term field CO2 fumigation experiments.

Dalmatian toadflax was included because it is one of a group of Eurasian weeds that threatens natural vegetation in the West, and it is the focus of a new global change experiment being conducted at the U.S. Department of Agriculture's High Plains Grasslands Research Station near Cheyenne, said Williams. He and co-investigators at the station are experimentally flooding the vegetation with elevated CO2 to examine how this weed responds in native prairie.

Yellowstone National Park provides an expansive laboratory belching enormous quantities of CO2 into the atmosphere and available to nearby vegetation.

The scientists are studying the effects near the Ochre Springs and Mammoth Hot Springs areas. Samples were also taken at control sites in areas having similar soil types and temperatures but not elevated CO2 levels.

"We believe that studying these plants will provide important insights into how global increases in atmospheric carbon dioxide concentration are likely to affect ecosystem functioning in the forest," said Sharma.

Sharma studied the isotope carbon 14 content of leaves near the carbon dioxide springs. "We used the C-14 content of the leaves to estimate the average carbon dioxide concentration during the growing season within the forest canopy moving away from the CO2 vents," she said.

Carbon dioxide from the vents does not have C-14 thus giving it a distinct radiocarbon signal from the background atmosphere, which does contain C-14. The radiocarbon content of plant tissue is proportional to average C-14 content of source air, allowing researchers to estimate the carbon dioxide concentrations in areas moving away from CO2 vents.

Scientists are also measuring the nitrogen percentage and carbon-to-nitrogen ratio in plants to assess how tissue quality and protein content are affected under elevated CO2 conditions.

Sharma said the measurement of carbon isotope values of lodgepole pine and Dalmatian toadflax shows responses to elevated CO2.

"Once our isotopic analysis is complete, we will be able to estimate whether stomatal conductance and/or photosynthetic capacity are being altered by changes in CO2 concentrations," she said. "After we obtain data on the nitrogen percentage and carbon-to-nitrogen ratio in these plants, we will also be able to predict how the forage quality may be affected in a future of globally increasing atmospheric CO2 levels."

Wyoming's natural places are treasures to be managed with great care for future generations, she noted. "Our study will help resource managers in Wyoming anticipate changes in natural ecosystems brought about by human activities at a global level. Such knowledge can be applied to properly sustain the goods and services provided by these natural ecosystems."

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Date: 1/26/07

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