Introduction and Site Description 45 



concentrations are similar in plants from site to site in spite of great 

 variations in soil concentration. In contrast, phosphorus concentrations in 

 plants are highest in the most productive sites. These data suggest that 

 phosphorus more strongly limits production than do other nutrients. 

 Fertilization experiments tend to confirm this hypothesis, as they result in 

 an increase both in production and in the phosphorus concentrations in 

 plants; other nutrients cause no change in concentration. 



Despite this limitation of phosphorus on plant productivity, it does 

 not act through altered photosynthetic capacity of each leaf. Instead, all 

 leaves produced have the same optimal photosynthetic capacity. The 

 limitation of nutrients appears to act by controlling the rate of production 

 of new leaves and may also influence the rate at which nutrients are 

 removed from older leaves. 



Vascular plants may lose a significant amount of potassium and 

 perhaps phosphorus by leakage onto the leaf surface. These nutrients, plus 

 those leached from standing dead, are subsequently washed off the leaves 

 and form the major nutrient input to the bryophytes. Once nutrients are 

 incorporated into bryophyte tissue, they are released slowly as 

 decomposition of these forms is very slow. Recycling may be speeded up 

 by the feeding of lemmings on bryophytes in winter. 



The spatial distribution of nutrients is in part controlled by lemming 

 activities. This control occurs in winter when lemmings build nests in 

 polygon troughs but forage in other areas as well. Most of the lemming 



PRECIPITATION 

 Ammonia Nitrite Nitrate 



20.3 



0.1 



2.7 



ARCTIC TUNDRA ECOSYSTEM 



Storage and 



undefined 



losses 



c= 



77.9 



n r 

 3.0 



U i.: 



ATMOSPHERE 

 CI69.3 Nitrogen Fixotion 



[)~2.4 Denitrification 



7.T JJ 



Nitrate 



Ammonia 



Dissolved 

 Organics 



Suspended Particulates 

 RUNOFF 



FIGURE 2-8. Nitrogen budget for coastal tundra at Barrow. All 

 units are mg N m~^ yr\ (After Barsdate and Alexander 1975.) 



