Lisa Pedicino M.S. 1997 Contact Information: Ms. Lisa Pedicino c/o Prof. Jon Pedicino College of the Redwoods, Eureka Campus 7351 Tompkins Hill Road Eureka, CA 95501 E-mail:c/o jon-pedicino@redwoods.edu

M.S. Thesis Title: CARBON ISTOPIC VARIATIONS IN 7 SOUTHWESTERN U.S. PLANTS FROM HERBARIUM COLLECTIONS OF THE LAST 150 YEARS School of Renewable Natural Resources The University of Arizona 1997 Abstract Since industrialization atmospheric CO2 concentrations have increased from 280 to 365 ppmv and d^13Cair has decreased from -6.5 to -8.2 ‰. These two trends have consequences for plant physiology. I examine d^13Cplant and physiological parameters in herbarium specimens of Atriplex confertifolia, Atriplex canescens, Ephedra viridis, Pinus edulis, Pinus flexilis, Juniperus scopulorum, and Quercus turbinella. For all species, I found relatively high and unsystematic variability. d^13C values for A. confertifolia and A. canescens varied by up to 7.9 and 9.5 ‰ respectively; d^13C values of these C4 shrubs are unsuitable for reconstructing d^13Cair, as previously claimed. d^13Cplant generally becomes more depleted except inP. edulis. Other calculated parameters such as D, Ci/Ca, Ci, and A/g have varying responses even among similar functional groups. Because much of the isotopic variability caused by interplant, intertree, intersite, and interannual differences is implicit, herbarium specimens are inadequate for precise detection of direct CO2 effects on plant physiology.