HR: 1340h
AN: PP43B-1267    [Abstracts]
TI: Plant Cuticle: A Geochemical and Biophysical Sensor of the Carbon Cycle
AU: * Upchurch, G R
EM: gu01@txstate.edu
AF: Texas State Univeristy, Deparment of Biology 601 University Drive, San Marcos, TX 78666, United States
AU: Marino, B D
EM: bmarinob@gmail.com
AF: Planetary Emissions Management, Inc., One Kendall Square Building 400, Cambridge, MA 02138, United States
AB: Plant cuticle--the decay-resistant outer layer of leaves and young stems—-is the most abundant identificable component of the plant fossil record next to pollen and spores and occurs in both megafossils and phytodebris. Plant cuticles provide major information on past levels of atmospheric CO₂ because of the inverse relationship between pCO₂ and Stomatal Index in many modern species. Some geochemical studies have used partially decayed fossil leaf material (referred to as "plant cuticle") to reconstruct changes in atmospheric δ ¹³C by means of the strong correlation, in modern plants, between atmospheric δ ¹³C and that of plant tissue. However, the occurrence within the same piece of fossil tissue of different chemical compounds with different isotopic signatures limits the accuracy of reconstructions, because decay under anaerobic conditions distorts the original isotopic values. A standard histochemical test for plant cuticle—-namely, high resistance to oxidation in chromium trioxide—- indicates the potential for isolating pure fractions of plant cuticle from the geologic record and using these fractions to reconstruct past changes in atmospheric δ ¹³C. Plant cuticle macerated in chromium trioxide is 3.5‰ more negative than whole tissue, an offset similar to that for other lipids and lignin. Preliminary isotopic analysis of fossil "cuticle" suggests that much, if not most, of the fossil "cuticle" reported in the geochemical literature may represent a mixture of cuticle, remnant cellulose, and other compounds. The offset between cuticle and whole tissue appears to be consistent for plants with C₃, C₄, and CAM photosynthesis, indicating that plant cuticle can be used to reconstruct the path of photosynthetic carbon fixation. Plant cuticle oxidized in chromium trioxide can be identified to genus and species through light microscopy and SEM, providing much greater taxonomic resolution for isotopic studies than is possible with bulk carbon and many biomarker compounds. In addition, fossil leaf cuticle can be analyzed for Stomatal Index by light microscopy prior to its combustion for isotopic analysis, so that the same piece of cuticle can potentially provide information on levels of atmospheric CO₂ and the isotopic composition of the atmosphere. Because dispersed plant cuticles can be analyzed with stratigraphic resolution close to that of pollen and spores, they can provide a high-resolution record of changes in the carbon cycle.
UR: http://www.agu.org/upchurchandmarino
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1055 Organic and biogenic geochemistry
DE: 3344 Paleoclimatology (0473, 4900)
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 4914 Continental climate records
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting