Photosynthesis 121 



calculated as described previously. The energy budget is solved for each 

 stratum, and the partitioning of energy exchange by convection and 

 transpiration is determined for stems and leaves. Transpiration is the re- 

 sultant relative saturation deficit which affects leaf water potential and 

 thereby leaf resistance and the carbon dioxide diffusion pathway. Photo- 

 synthesis on a leaf area basis is calculated for sunlit and shaded leaves 

 and stems in each stratum. In this model the internal resistances depend 

 on solar radiation and temperature. 



Solar Absorbed, 



J IT) s 



Net Photosynthesis, 

 rrig COj dm^ hr'' 



0600 1200 laoo 



0600 1200 1800 



Leaf Water Potentiol, bars Leaf Resistance, s cm' Meon Leaf Temperature, °C 



0600 1200 1800 



0600 1200 1800 



Solar Time 



0600 1200 1800 



FIGURE 4-10. Isopleths showing the simulated daily course of various 

 plant responses to environmental conditions through the canopy for a 

 5-day period beginning 15 July 1971. (After Miller et al. 1976.) 



