170 F. S. Chapin III et al. 



FIGURE 5-13. Seasonal course of (a) percentage 

 nitrogen and calcium and (b) standing crop of ni- 

 trogen, calcium, and biomass in Du^onixSi sampled 

 from moist meadow tundra. (After Chapin et al. 

 1975, Chapin 1978.) 



days before the maximum standing crop of biomass is achieved. The 

 most rapid transfer of nitrogen to the shoots occurs during the first three 

 weeks of the growing season (Figure 5-13), at which time the activity of 

 old roots would be minimized by poor aeration and low temperatures. It 

 is probable that most of the early-season aboveground nitrogen and 

 phosphorus comes from stored reserves rather than from current-season 

 absorption by roots as demonstrated for upland tundra (Chapin et al, 

 1980). The bulk of all plant nutrients are located below ground (Table 

 12-3), such that seasonal changes in aboveground standing crop involve 

 at most 20% of the total plant nutrient content. 



Precipitation and dew drip continually leach nutrients (particularly 

 potassium) from shoots at a rate that depends upon local weather condi- 

 tions and the solubility of the different elements. Nitrogen and phos- 



