166 F. S. Chapin III et al. 



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FIGURE 5-10. Predicted rate of phosphate absorption per gram of 

 Dupontia fisheri root during the 1973 growing season, a) Measured phos- 

 phate absorption capacity of roots corrected for percentage of root bio- 

 mass present in thawed soil (calculated from Dennis 1977). b) Absorp- 

 tion rate in a corrected for soil temperature (MacLean 1973). c) Absorp- 

 tion rate in b corrected for soil solution phosphate concentration (Barel 

 and Barsdate 1978). d) Predicted cumulative phosphate absorption per 

 gram of root during the growing season. Vertical arrow indicates date 

 when net downward translocation of phosphorus from shoots to below- 

 ground storage organs begins. (After Chapin and Bloom 1976.) 



