120 



L. L. Tieszen et al. 



SIMULATION ANALYSIS OF PHOTOSYNTHESIS 

 AND VASCULAR CANOPY INTERACTIONS 



Models 



Vascular Plant 



Previous discussions of photosynthesis have considered the physio- 

 logical responses of single leaves, tillers or moss mats to independent 

 biotic and abiotic factors. In plant communities these factors do not 

 operate independently. They result from complex feedbacks involving 

 regional cHmate, canopy structure, and the process of carbon dioxide up- 

 take. In an attempt to quantify these relationships and to determine their 

 relative and absolute importance, they have been incorporated into an in- 

 teractive model called Stand-Photosynthesis which is basically an out- 

 growth of models discussed earlier (Miller and Tieszen 1972, Miller et al. 

 1976, Stoner et al. 1978b). 



The stand photosynthesis model is based on the fluxes of carbon 

 dioxide, water, and heat for a single leaf located in the canopy in profiles 

 of direct and diffuse solar and infrared radiation, wind, air temperature, 

 and vapor density. The canopy consists of horizontal strata of live and 

 dead leaves, stems, and reproductive structures. The vegetative canopy 

 produces profiles of solar and infrared radiation, by intercepting, ab- 

 sorbing, and emitting radiation, which are calculated for each stratum. 

 Similarly, the canopy effects on wind, air temperature, and humidity are 



V 1.2 



o 

 o 



0) 



o 

 o 



0.8 



0.4- 



-0.4 



0400 0800 1200 1600 2000 2400 0400 0800 1200 1600 2000 2400 



Solor Time 



FIGURE 4-9. Comparison of net CO2 exchange from field cuvette (o), 

 simulation (x), and aerodynamic estimates (%). The aerodynamic data 

 represent flux from the atmosphere only. The cuvette measurements and 

 simulations are for vascular plants. Cuvette data from Tieszen (1975), 

 aerodynamic data from Coyne and Kelley (1975), simulations from 

 Miller et al. (1976). 



