HR: 0800h
AN: PP51B-1334    [Abstracts]
TI: Stomatal Frequency and Atmospheric CO2: a Model Based on Photosynthesis and Gaseous Diffusion
AU: * Roth-Nebelsick, A
EM: anita.roth@uni-tuebingen.de
AF: Institute for Geosciences University of Tuebingen, Sigwartstr. 10 , Tuebingen, D-72119 Germany
AU: Konrad, W
EM: wilfried.konrad@uni-tuebingen.de
AF: Institute for Geosciences University of Tuebingen, Sigwartstr. 10 , Tuebingen, D-72119 Germany
AB: Gaseous exchange in land plants occurs via micropores on the plant surface, the stomata. The stomatal frequency (SF) of leaves has attracted considerable interest with respect to increasing atmospheric CO2 since Woodward (1987) demonstrated that this parameter changes inversely with CO2 in various species. The response is due to 1) individual phenotypic plasticity and 2) evolutionary change, depending on the considered time scale. The SF-CO2 response is regarded to represent a valuable device for determining past atmospheric CO2 concentration and SF data from fossil plant material are therefore often used as CO2 proxies. There are, however, numerous difficulties which have to be considered, such as: 1) high variance of the data, especially for fossil material, 2) interspecific differences of the response, 3) the CO2 ceiling (= weak or no response under CO2 concentration higher than ambient) and 4) differences between short-term and long-term responses. Although processes related to plant gaseous exchange are assumed to represent the causal basis for the response, no clear explanatory model has yet been proposed and even doubts have emerged about the real existence of this phenomenon. In this contribution it is shown that results obtained with a model based on diffusion and assimilation suggest that the SF-CO2 response is a structural adjustment of maximum stomatal conductance. The results 1) offer a clear explanation for the often observed weak response of stomatal frequency to CO2 levels higher than ambient, 2) provide a simple equation for calculating ancient CO2 levels from stomatal data, and 3) can contribute to predictions concerning plant reactions to elevated CO2 levels in the future.
DE: 9604 Cenozoic
DE: 3344 Paleoclimatology
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting