The Microflora 271 



of the yeast population present, and these counts are likely conservative. 

 The single taxon identifled frequently occurs as an epiphyte and the rela- 

 tively large biomass of yeast on polygon rims (5.2 x 10"' g m"') probably 

 exists on the abundant mosses. In other high latitude sites yeasts occur at 

 about the same level of abundance, also commonly as epiphytes (Baker 

 1970a, b, Dowding and Widden 1974). 



Seasonal averages of fungal density, expressed as mycelial length per 

 gram of soil, in the upper 1 to 2 cm of soil range from 496 m (gdw soil)"' 

 in polygon troughs to 1445 m (gdw soil)"' on the rims of low-centered 

 polygons (Table 8-1). Although fungal abundance in the more favorable 

 units is similar to that found in Irish blanket bog and in mesic to dry arc- 

 tic meadows of Norway and Canada (Dowding and Widden 1974), it is 

 much lower than in other Biomes. In woodland soils it is not uncommon 

 to find 7000 m (gdw soil)"' or more in organic soil horizons (Parkinson 

 1971). In surface soils of the coastal tundra at Barrow, however, fungi 

 are still an important component of the microflora biomass and their 

 biomass in the top 1 to 2 cm ranges from 0.38 g m"^ in polygon troughs to 

 1.87 g m"^ on the better-aerated rims (Laursen 1975). In general, the rela- 

 tive proportions of fungi and bacteria in soils of polygon rims resemble 

 those observed in temperate soils more closely than do proportions in 

 other microtopographic units (Table 8-1). Conversely, the dominance of 

 bacteria in the wet meadows and polygon troughs suggests that decom- 

 position in wet tundra soils is governed by bacteria to a greater degree 

 than in many soils examined in other Biomes. 



Although mycelial densities per gram of substrate are generally two 

 to three times higher in litter and standing dead than in soils, somewhat 

 more fungal biomass is present in soil because of the greater density of 

 substrate. Fungal densities per gram of substrate in litter and standing 

 dead vegetation are similar in all microtopographic units examined with 

 the exception of the basins of low-centered polygons (Table 8-1). On rims 

 of low-centered polygons, as well as in wet meadows and polygon 

 troughs, mycelial densities in both litter and standing dead vegetation 

 range from about 2000 to 2700 m gdw"' of substrate. In basins the aver- 

 age seasonal values for fungal density are 1038 m gdw"' in litter and 669 

 m gdw"' in standing dead vegetation. The relative inhospitality of basins 

 for the decomposer flora is evident in the dead vegetation as well as the 

 soil. Much of the difference in relative distribution of fungal biomass in 

 litter and standing dead vegetation across microtopographic units (Table 

 8-1) is attributable to differences in amounts of substrate, not fungal 

 densities. 



Although algae are not members of the decomposer community they 

 are considered here as a constituent of the total microflora. Volumes of 

 blue-green, green and diatomaceous algae in the moss and surface soil 

 do not show the same variability among microtopographic units as do the 



