332 P. W. Flanagan and F. L. Bunnell 



E 



28 



26 

 24 



22 



20 



18 



16 



14 



12 



10 



8 



6 



4 



2 







fJ3'" 



Nitrogen 



xn. 



ABODE 



14 

 1.2 



1.0 

 0.8 



0.6 

 0.4 

 0.2 

 0.0 



rS'" 



Phosphorus 



n 



ABODE 



FIGURE 9-13. Total and available pools and potential 

 release rates of nitrogen and phosphorus in the soil cal- 

 culated for the wet meadow. A) Total amount of nutri- 

 ent to 20 cm. B) Amount available including dissolved 

 and exchangeable (resin-extractable) phosphorus 

 (Flint and Gersper 1974, Barel and Barsdate 1978). C) 

 Amount of nutrient in an average standing crop of mi- 

 crobial tissue to 7 cm. D) Potential annual release 

 from tissue assuming 18.1 g m~^ microbial biomass, 

 5.0 generations, and no internal microbial mineral re- 

 cycling. E) Potential annual release calculated from 

 the nutrient content of the material undergoing decay. 



Without including annual input to the system from rain and nitrogen fix- 

 ation (Chapter 7) there appears to be more than adequate nitrogen for 

 plant growth in the coastal tundra at Barrow. The amount of nitrogen 

 immobilized by the average standing crop of microorganisms (0.8 g m"^) 

 is almost insignificant in terms of available nitrogen plus that generated 

 by decomposition. 



The situation is quite different, however, in the case of phosphorus. 

 The average amount of available phosphorus is small, as is the amount 

 of phosphorus released annually in decay processes. The phosphorus im- 

 mobilized in an average standing crop of microbial tissue is greater than 

 the sum of labile pool plus the annual input via decay (Figure 9-13), sug- 

 gesting a profound influence of microorganisms on availability of phos- 

 phorus in the system. Because tundra microorganisms, except for their 

 resistant propagules, die off each year, they 1) release a relatively large 

 quantity of phosphorus to the soil annually, and 2) are taking phos- 

 phorus from the system at levels that are greater than the normal size of 



