9418269 Leavitt This research is based on the assumption that changes in atmospheric CO2 concentrations over the past 40,000 years can be quantitatively measured by determining the stomatal density and stable-carbon isotope composition of modern and ancient plant leaves, particularly leaves preserved in packrat middens in the western U.S. To overcome the problem of separate effects of climate and CO2, PI intends to employ analog approach by using leaves from different latitudes and/or elevations to maintain constant climate. Samples from the same latitude but different ages and elevations will allow determination of whether attitudinal gradients in stomatal density and carbon isotopes are the same in high and low CO2 periods. Ground truthing will be through analysis of modern living samples and herbarium samples. Possible implications of the research include determination of the relative effects of CO2 concentrations and climate influences on vegetation change, refinement of carbon cycle and hydrological models during deglaciation, confirmation of CO2 and carbon isotope shifts identified in earlier studies, and enhanced understanding of CO2 variations in the evolution and distribution of C4 plant.
