Primary Producers 237 



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1600 2000 2400 0400 0800 



a) 14 and 15 July. 



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Totol Rod. = 107 ly day" 



Meon Temp.- 0.4°C 



(o) Carex oquatilis = 20 mg CO2 dm^ day"' 



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1200 1600 2000 2400 0400 0800 

 Time , hr 



b) 25 and 26 A ugust. 



FIGURE 5-34. Daily course of net CO2 uptake by Carex 

 aquatilis of chamber temperature, and of insolation. The 

 hourly values for photosynthesis are means of five determina- 

 tions (Tieszen, unpublished data.) 



Nutrients 



Added nutrients had no immediate effects on plants, but over longer 

 periods added nutrients did increase the plant biomass. Ten years after 

 fertilization of terrestrial plots began at Barrow, the biomass had doubled 

 (Dennis et al. 1978). The exact mode of action of nutrients was not clear, 

 however, for Johnson and Tieszen (1973) found that fertilization of 

 terrestrial plants did not affect either chlorophyll concentrations or 

 photosynthetic and carboxylation rates per unit of biomass. Fertilization 

 with either P alone or P + N did affect leaf area, canopy height and plant 

 density. From these and other data, Bunnell et al. (1975) suggest that the 

 effect of added phosphorus is not on photosynthesis but on the allocation 

 of carbohydrates to leaf growth. 



Under natural conditions, the plants are closely tuned to the 

 prevailing climate and rate of nutrient supply. Therefore, added nutrients 



