Biophysical Processes and Primary Production 



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20 - 



10 



FIGURE 3-11. Seasonal progression of incoming 

 solar irradiance (Q), quantity reflected up from 

 the canopy (Q,.), quantity intercepted by the 

 canopy (Qj), quantity absorbed by the soil (Q^), 

 quantity absorbed by the canopy (QJ, and quanti- 

 ty absorbed by the photosynthetic tissue (QJ and 

 of downward and upward infrared irradiance (Q). 

 The net infrared loss is partitioned by source. 



the coastal tundra at Barrow (Miller and Tieszen 1972, Miller et al. 1976, 

 Ng and Miller 1977), absorptances of 0.5 for live leaves and stems and 

 0.4 for dead leaves were used. Chlorophyll concentrations in the vegeta- 

 tion at Barrow were similar to those of temperate plants (Tieszen 1972b). 

 Absorbed solar radiation per unit leaf area was highest at the top of 

 the canopy throughout the day and through the growing season (Figure 

 3-10). However, even at the top of the canopy absorbed irradiances were 

 near or below light saturation for photosynthesis, indicating that photo- 

 synthesis was usually light-limited (Chapter 4). One might anticipate 

 greater leaf areas at canopy levels where photosynthesis was greater. But 

 most of the live leaf area was concentrated at the bottom of the canopy 

 and most of the solar radiation on a ground area basis v/as absorbed near 

 the ground surface. 



