The Microflora 269 



soils as well, it appears that total microfloral biomass in the upper 7 cm 

 of soil ranges from 12 to 20 g m'\ with the greatest amounts of biomass 

 in wet meadows and polygon troughs, less on rims of low-centered poly- 

 gons, and least in basins of low-centered polygons. These values are con- 

 siderably less than those observed for temperate grasslands. From the 

 data of Clark and Paul (1970) the microfloral biomass in a grassland soil 

 to a depth of 10 cm is 77 g m"', of which only 31% is bacterial. 



Within the tundra environment the suitability of the various micro- 

 topographic units for different decomposer groups can be assessed by 

 comparing the relative levels of average seasonal biomass of a particular 

 group found in the different units (Table 8-1). Data for the aerobic soil- 

 inhabiting organisms (fungi, yeasts and plateable bacteria) are presented 

 to a depth of 2 cm only; during most of the summer season the activity of 

 these organisms is concentrated in the surface layers of the soil. Eukary- 

 otic decomposers (fungi and yeasts) are most abundant on rims of low- 

 centered polygons (Table 8-1), which show somewhat greater concentra- 

 tions of oxygen in soil solution. Furthermore, rims frequently support 

 the Carex-Poa vegetation type in which primary production is domin- 

 ated by mosses. Because mosses are richer in aromatic compounds than 

 graminoids, and the decomposition of large molecular weight aromatics 

 proceeds largely through fungal metabolism, the predominance of 

 mosses may favor fungal dominance. Antagonism between yeasts and 

 bacteria in tundra soils is suggested by these comparisons, and further 

 corroborated by the seasonal courses of biomass for these groups. 



In wetter microtopographic units the relative abundance of soil 

 fungi decreases while that of bacteria increases, apparently in response to 

 increasingly anaerobic conditions. Reasons for the particularly marked 

 reduction of the decomposer flora in basins of low-centered polygons are 

 unclear but it may be associated with low levels of available phosphorus. 

 The relatively high algal biomass in the basins is composed largely of dia- 

 toms. Methodologies involved may have included a significant accumu- 

 lation of dead diatomaceous cells, which also could be associated with 

 low potential for decomposition rather than higher algal production. 



Bacterial plate counts from the relatively productive polygon 

 troughs and meadows (Table 8-2) are similar to those from mires and 

 meadows of other arctic and subarctic locations (Parinkina 1974, Clar- 

 holm et al. 1975, Widden 1977), but are commonly one order of magni- 

 tude lower than those reported for temperate grasslands (Paul et al. 

 1973). Conversely, direct bacterial counts tend to be higher than in forest 

 or grassland soils, but are broadly similar to counts from other tundra 

 soils (Parinkina 1974). Measures of total bacterial biomass are thus 

 similar to those at other tundra sites, and because of the relatively small 

 size of tundra bacteria the biomass estimates made from direct counts are 

 similar to those of more temperate regions as well. When plate counts are 



