Shikha Sharma (left) and David Williams collect leaf samples from lodgepole pine for radiocarbon and stable isotope analysis. [See Related Image.]
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The large and rapid rise in atmospheric carbon dioxide (CO2) concentration due to human activity and associated global warming has the potential to alter Earth's climate system and affect terrestrial ecosystems. An important source of uncertainty in predictions about atmospheric change is how plants will respond to increasing atmospheric carbon dioxide and how climate changes interact with rising CO2 concentrations to affect plant growth and photosynthesis. We are examining effects of elevated CO2 on photosynthesis of trees and invasive weeds in Yellowstone National Park by taking advantage of natural gradients in atmospheric CO2 concentration produced near geological CO2 springs. We are tracing the unique radiocarbon (14C) signature in CO2 taken up by these plants from geological sources as a way to characterize the long-term exposure of plants to elevated CO2. Photosynthetic responses of plants are then estimated from the stable carbon (13C) and oxygen (18O) isotope ratios in plant leaves.
Our initial observations reveal the potential for contrasting responses to elevated CO2 between the dominant tree species in Yellowstone National Park--the lodgepole pine, and a noxious invasive forb--the Dalmation toadflax. Further investigation involving more widespread sampling and experimental manipulations of soil resources will provide valuable information about how vegetation in the Greater Yellowstone Ecosystem is likely to respond to future atmospheric changes. Of particular relevance is how elevated CO2 will alter the nutritional quality of vegetation sustaining Bison, Elk and other key wildlife species in Yellowstone.
This research was supported by a National Science Foundation EPSCoR (Experimental Program to Stimulate Competitive Research) Program grant EPS 99-83278, Wyoming EPSCoR Cooperative Agreement, project director Randolph V. Lewis. Dr. David Williams was an EPSCoR-hire under this grant to continue and enhance the strong research area of the Stable Isotope Facility at the University of Wyoming. (Date of Image: Dec. 2005-2006)