1. General Model Information

Name: Gas-Flux canopy photosynthesis model

Acronym: GAS-FLUX

Main medium: air+terrestrial
Main subject: hydrological, biogeochemistry
Organization level: Ecosystems
Type of model: compartment model
Main application:
Keywords: photosynthesis, canopy structure, radiation interception,


Prof. Dr. John D. Tenhunen
Universitaet Bayreuth
Bayreuther Institut fuer terrestrische Oekosystemforschung

95440 Bayreuth

Phone: +49-921-55-5620
Fax : +49-921-55-5799
email: John.Tenhunen.@bitoek.uni-bayreuth.de



contents of the model
The model computes vertical profiles of leaf temperature, radiation penetration, water and CO_2 exchange of a spatially homogeneous vegetation canopy. The canopy is characterized by (typically around 10) horizontal layers that are assumed homogeneously with respect to leaf photosynthesis and structural parameters. The model is parameterized (each layer seperately) with canopy structural data (leaf area, leaf anufis/gle, projected stem area, stem angle) and leaf photosynthesis parameters of any species. A layer is only allowed to contain a single species, but mixed species can be modeled as a set of merged canopy layers. To run the model, time series of above canopy irradiation, air temperature, air humidity and wind speed are required.
principles of the model
Canopy photosynthesis is integrated over total leaf area using the methods developed in Farquhar and von Caemmerer (1982), stomatal conductance is computed after Ball et al. (1987) and Harley and Tenhunen (1991). Light interception follows Duncan et al. (!967) including the Wilson/Reeve ratio based on inclined point quadrats (Warren Wilsion 1960). The method assumes the sun as a point source for radiation. The energy balance is solved for a vertical transect through the canopy by seperately considering direct and diffuse shortwave, longwave radiation as well as the feedback between stomatal conductance, surface temperature and heat loss from the canopy layers.

Author of the abstract: UFIS - Environmental research information system

II. Technical Information

II.1 Executables:

Operating System(s): DOS, UNIX Type of computer: PC, Workstation RAM required: minimal Disc space: minimal Portability onto other systems: any Peripherical software required: none

II.2 Source-code:

Programming Language(s): FORTRAN, C

II.3 Manuals:

II.4 Data:

III. Mathematical Information

III.1 Mathematics

III.2 Quantities

This is a list of model quantities sorted by their characteristics with hypertext links for more details.

III.2.1 Input

III.2.2 Output

IV. References

Farquhar, G.D., von Caemmerer, S., 1982.
Modelling of photosynthetic response to environment., Encyclopedia of Plant Physiology, 12B, Lange, O.L., Nobel, P.S., Osmond, C.B., Zieufis/gler, H., (editor(s)), Springer, Berlin-Heidelberg-New York, pp. 549-587.

Harley, P.C., Tenhunen, J.D., 1981.
Modelling the Photosynthetic response of C3 Leaves to Environmental Factors. In: Modelling Crop Photosynthesis - from Biochemistry to Canopy, CSSA Special Publications, 19, American Society of Agronomy and Crop Science Society of America, 677p.

Tenhunen, J.D., Siegwolf, R.A., Oberbauer, S.F., 1994.
Effects of phenology, physiology, and gradients in community composition, structure, and microclimate on tundra ecosystems CO_2 exchange. In: Ecophysiology of Photosynthesis. , Ecol. Studies, 100, Schulze, E.D.; Caldwell, M.M. (editor(s)), Springer, Berlin-Heidelberg-New York, pp. 431-460.

V. Further information in the World-Wide-Web

VI. Additional remarks

The variable 'CO_2 Fixation' is used as input variable in the growth model TRAGIC.

Additional information
Last review of this document by: T. GabeleNov 21th 1997
Status of the document:
last modified by Tobias Gabele Wed Aug 21 21:44:43 CEST 2002

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