246 



P. L. Gersper et al. 



TABLE 7-6 



Ratios of Total Carbon to Organic Phosphorus in Soils of 

 Different Microtopographic Units and Associated Vegeta- 

 tion Types and States of Organic Matter Decomposition 



ND indicates no data. 



(C:Po), appear unfavorable for mineralization. The C:N ratio is close to 

 20:1 throughout the range of undisturbed soils in the tundra at Barrow. 

 In general, C:N ratios below 20:1 produce net mineralization of nitrogen 

 and ratios greater than 20:1 lead to the microbial transformation of inor- 

 ganic nitrogen into organic forms, or immobilization (Frissel and Van 

 Veen 1978). The ratios of carbon to phosphorus are calculated from or- 

 ganic rather than total phosphorus since a significant fraction of the total 

 phosphorus is present in inorganic form rather than in the microbial sub- 

 strate. The lowest C:Po ratios, which indicate the most favorable condi- 

 tions for mineralization, are between 300 and 400:1 (Table 7-6). These 

 values occur in the surface soils of all microtopographic units except rims 

 and basins of low-centered polygons, and to depths of 10 to 15 cm in the 

 polygon troughs. Ratios generally increase with depth, reaching values 

 above 1000:1 in the 15- to 20-cm depth of rim soils and the 10- to 20-cm 

 section of the basin soils. Cosgrove (1967) considered 0.2% (290:1) as the 

 critical level of phosphorus in organic matter. Kaila (1949) found no net 

 mineralization or immobilization of phosphorus from the decomposition 

 of organic material with 0.3<!7o P (194:1). It would appear that weak net 

 immobilization of nitrogen and strong net immobilization of phosphorus 

 should occur in the soils of the coastal tundra at Barrow. 



However, mineralization must exceed immobilization in the soils 

 since the net inputs are far too low to maintain the observed rates of 

 plant production (Flint and Gersper 1974). Net mineralization could 

 result from decreases in microbial efficiency as compared with values 

 found in temperate soils. However, the tundra microflora appear rela- 



