Introduction and Site Description 41 



polygon ridges, which arc consequently fertilized. This may be the only 

 mechanism for nutrient movement onto the higher parts of the tundra. 



Decomposition 



Within 3 years of death, plant materials at Barrow lose 60% of their 

 weight (see Brown et al. in press for details). Half of this loss occurs in the 

 first year from Carex aquatilis (26.6%) and Eriophorum angustifolium 

 (21.1%). Most of the first-year loss is by leaching of organic matter, but 

 inorganic nutrients may also be rapidly lost. For instance, 70 to 80% of the 

 phosphorus and potassium are lost during the first year. In contrast, 

 calcium is immobilized in the cell walls and is lost very slowly. The pattern 

 of total weight loss after the first year is the sum of two exponential decay 

 rates; one rate is 49% per yr for rapidly metabolized compounds (ethanol 

 soluble), the other rate is 1 1 % per yr for recalcitrant compounds. 



The factors controlling the rates of decomposition at the Barrow site 

 include the duration of freezing, the low pH, the low oxygen 

 concentrations in the soil, the low amounts of available nitrogen and 

 phosphorus, and the effect of the low temperatures on microbial processes. 

 Even though water is abundant, the standing dead plant parts are too dry 

 for rapid decomposition. Thus, the loss of weight in standing plants is 4 to 

 5% per yr but this increases to 7 to 10% per yr once the material enters the 

 litter layer. 



The amount of carbon dioxide evolved from the soil was twice as high 

 on polygon rims and in troughs as in polygon basins; evolution from 

 meadow soils was even higher. Over a period of 85 days (26 June to ID 

 September) the evolution from meadow soils matched the net primary 

 production (159 g C m"^). Despite the anaerobic soils, little methane 

 leaves the soil. Respiration, and therefore decomposition, is increased 

 when lemmings are abundant or where vehicles have pressed down the 

 dead vegetation. 



Both bacteria and fungi are abundant in the litter and soils; in fact, it 

 is not their biomass but their activity that limits decomposition. Bacterial 

 numbers, 10^ or 10'" cells (g dry weight) " ' estimated as a direct count, are 

 similar to those in temperate soils. Aerobic plate counts fall in the range 

 0.5 to 10 X 10** cells g"'. Mycelia length (per g dry wt) is from 200 to 2700 

 m, but despite this amazing length the fungal biomass is only a third to a 

 quarter that of the bacteria. 



Invertebrate Biomass and Production 



The major invertebrates in Barrow soils are Nematoda, annelid 

 worms (Enchytraeidae), mites (Acarina), springtails (Collembola), and 



