476 F. S. Chapin III et al. 



TABLE 12-5 Nutrient Turnover Rate in Various Compart- 

 ments of the Moist Meadow Vegetation Type 



Net turnover rate (% of pool yr"')* 



Compartment N P K Ca Mg 



Dissolved soil inorganic 6,089 21,919 371 96 54 



♦Assumes a one-way transfer of material. The actual turnover rate will be much 

 greater in pools where there are multiple paths of nutrient flow through the 

 compartment, as in soil organisms. 



tPool nonexistent. 

 **Not measured. 



tundra sites (Chapter 5). Hence, the role of decomposition and nutrient 

 mineraUzation is extremely important in the cycling of these elements 

 and in the functioning of the system in general. 



Nutrient turnover rates of soil organic matter are 5 orders of magni- 

 tude lower than those of the soluble soil pools (Table 12-5). The turnover 

 times ( = total/input) for carbon, nitrogen and phosphorus averaged for 

 the top 20 cm of soil organic matter are 220 years for carbon, 480 years 

 for nitrogen and 240 years for phosphorus. This compares with an aver- 

 age world carbon turnover time of 40 years (Schlesinger 1977). Such 

 turnover estimates mask complexities associated with different soil or- 

 ganic fractions, each with distinct turnover times (Jenkinson and Rayner 

 1977). The slow turnover of organic nutrient pools in the soil seems re- 

 sponsible for the slow overall cycling of nutrients in the coastal tundra at 

 Barrow. Slow nutrient cycling characterizes high latitude ecosystems gen- 

 erally (Jordan and Kline 1972, Babb and Whitfield 1977, Dowding et al. 

 1981). Soluble inorganic phosphorus and nitrogen pools are extremely 

 small and turn over rapidly (Table 12-5), contributing to microorganisms 

 and vascular plants while receiving input from a variety of sources. The 

 soluble nitrogen must be replenished at least 60 times in the course of the 

 growing season to supply the quantity absorbed by plants. Soluble phos- 

 phorus must be replenished 220 times a season, an average of three times 

 a day. The soluble pools for mineral cations turn over less rapidly (Table 

 12-5). 



Although the dissolved nutrient pools are small, they are presumably 

 in equilibrium with larger exchangeable pools. The input into the dis- 



