PARENT SESSION
Symposium #26: Gasping for CO₂: Ecological Effects of Past Variations in Atmospheric CO2.

Organized by: JW Williams and S Cowling
Thursday, August 8. 9:00 AM to 11:30 AM. Turquoise Ballroom, TCC.

Ecophsyiological and morphological changes in plant macrofossils in response to CO₂ shifts during the terminal Pleistocene.

Van de Water, Peter^*,1, ¹ Institue of Arctic and Alpine Research, Boulder, CO

ABSTRACT- Low atmospheric CO₂ concentrations during the full glacial differentially affected the physiology and morphology of past vegetation. Carbon isotopic analysis along with morphological measurements of macrofossils from packrat middens provides a unique record of these plant responses to low CO₂ conditions. Physiological and morphological changes were observed and classified using broad-based plant traits. For example, in the species tested stable carbon isotope values show increased discrimination and decreased water-use efficiency during full-glacial conditions. During the same period, the number and density of stomata on leaf surfaces increased, while the size of the photosynthesizing plant organ was reduced. These responses differed in magnitude among species showing different photosynthesis structures such as needled conifers (Pinus spp.), scaled-leaved conifers (Juniperus), versus stem photosynthesizing species (Ephedra). Changes in the distribution of species with these plant traits during the ice age is one measure of the ability of past plant populations to adapt to low atmospheric CO₂ conditions.

KEY WORDS: packrats, stomata, ¹³C, CO₂