The Soils and Their Nutrients 245 



and phosphorus because of the high level of conservation of incoming 

 nutrients. Losses to denitrification do not eHminate the positive balance 

 for inorganic nitrogen. When organic and inorganic forms are con- 

 sidered jointly, there is a net loss of both nitrogen and phosphorus from 

 the combined activity of the abiotic processes of precipitation and leach- 

 ing. However, the transformation of atmospheric nitrogen by nitrogen- 

 fixing organisms into a form available to the rest of the system leads to a 

 gain in total system nitrogen. Apparently, a net phosphorus loss has oc- 

 curred, as has been documented in bog tundras of Glenamoy and Moor 

 House (Heal et al. 1975, Moore et al. 1975). 



TRANSFORMATION AND TRANSPORT OF 

 NITROGEN AND PHOSPHORUS WITHIN THE SOIL 



The preceding discussion presented the major pathways by which 

 the total amounts of nitrogen and phosphorus in soils are increased or 

 decreased. Changes in the locations and forms of these nutrients within 

 the soil are also important in determining the supply available for biotic 

 processes. The following section describes the major transformations of 

 nitrogen and phosphorus that occur in the soils of the coastal tundra at 

 Barrow and their transport within the soils. 



Mineralization and Immobilization 



Since plants take up nitrogen and phosphorus in inorganic forms 

 and return these nutrients to the soil bound in organic matter, the process 

 of remineralization must be a major source of inorganic nitrogen and 

 phosphorus in any soil close to a steady state. Mineralization, the release 

 of inorganic nutrients from dead organic material by microbial action, 

 occurs whenever the concentrations of these nutrients in the organic ma- 

 terial are greater than those necessary to support the production of new 

 microbial biomass. As summarized by Frissel and Van Veen (1978), the 

 net mineralization rate is controlled by the microbial decomposition rate, 

 the concentrations of organic nitrogen and phosphorus in the material 

 being decomposed and in the microbial biomass being produced, and the 

 efficiency of the microbial population, i.e. the ratio of microbial biomass 

 produced to organic matter decomposed. For any given ratio of mineral- 

 ization to decomposition, the rate of release or uptake by the microflora 

 will be affected by all the factors that control decomposition rate (Chap- 

 ter 9). 



The nutrient levels in the organic matter in soils, expressed by the 

 ratios of carbon to nitrogen (C:N) and carbon to organic phosphorus 



