New Phytologist Volume 132, Issue 2, Pages 235-245 February 1996 |
|
Analysis of stomatal CO2 uptake by a three-dimensional cylindrically symmetric model T. Vesala1, T. Ahonen1, P. Hari2, E. Krissinel3 and N. Shokhirev4 1Department of Physics, P.O. Box
9, FIN-00014, University of Helsinki, Finland Received for publication June 12, 1995; Accepted October 26,
1995 |
|
|
| Abstract |
|
|
| A numerical model is introduced that solves the steady-state diffusion
equation for a single stoma and the mesophyll surrounding. This system has
cylindrical symmetry, and diffusive transport of carbon dioxide in the gas
phase is coupled with transfer in mesophyll along with a photosynthetic
sink rate and respiratory production rates. The mesophyll is treated as a
continuously distributed liquid phase, and the photosynthetic rate is
determined by the carbon dioxide concentration, the photosynthetic photon
flux density and the chlorophyll concentration. Photorespiration is
proportional to the photon flux density, and dark respiration is assumed
to be constant. The model offers a rigorous way to investigate the roles
of physics and geometrical structure in stomatal gas exchange. Lateral
(radial) diffusion and differences between hypostomatous and needle-like
leaves are analysed with special attention. To yield realistic stomatal
behaviour, the model requires that the diffusion coefficient describing
mesophyllic transport must be somewhat larger than carbon dioxide
diffusivity in pure liquid water. The mesophyllic carbon dioxide
concentration slopes sharply towards a constant value as a function of
distance from the surface of a sub-stomatal cavity. The optimal placement
of chlorophyll is close to the surface containing stomata. |
| Key words |
|
|
| Diffusion, CO2 exchange, CO2 concentration
profile, physics of stomata, needle. |