Carbon and nitrogen isotopic ratios of pollen plants: a tool for paleovegetations reconstruction?
by
Chantal Descolas-Gros
CNRS Institut des Sciences de l'évolution Paléoenvironnements et Palynologie Université de Montpellier II CC061 34095 Montpellier cedex 05

Continental paleoclimatic reconstructions are based on vegetation changes. They are linked to climatic parameters. Pollen gives access to informations on the vegetation. The composition in stable carbon isotopes of the organic matter synthesised is different for plants that occurred in hot and dry climates from those of temperate species. In lacustrine paleosediments, shift of ?13C values of organic carbon is usually interpreted as vegetation changes, but values of bulk organic carbon may integrate aquatic and organic decomposed material .The purpose of this poster was to examine if stable carbon isotopic ratios of pollen reflected the main pathways of photosynthetic carbon fixation (C3 and C4 photosynthesis principally), the variations of associated parameters (C/N, ?15N); the scales of variations observed inside a photosynthetic type. ?13C, C/N, ?15N values of pollen grains belonging to different plant species (trees, herbaceous no poaceae, poaceae) were measured. Most of these temperate species are C3 plants with ?13C values between -28,6‰ and -21,7‰, the C4 plants have more positive values between -15,9‰ and -10‰. These results corroborate the interest of such measurements to differentiate for example C4 poaceae from C3 ones. Inside the same genus or the same species data variability is studied. Chemical treatment (acetolysis) of pollen grains induces a lowering of the values. These preliminary results are intended to help calibrate the pollen grains ?13C of modern plants in order to use ?13C of fossil pollen grains to reconstruct paleovegetation variability responses to climatic factors.

Date received: May 28, 2001

Copyright © 2001 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # cahr-19.