288 F. L. Bunnell et al. 



graphic units. Temperature again exerts its greatest influence early and 

 late in the season, but may be a controUing influence throughout the 

 growing season in moist, concave microtopographic units. 



Marked differences in bulk densities among soils of different micro- 

 topographic units modify the pattern of control for soil organisms. 

 Again, enhanced substrate quality at snowmelt and late season leaching 

 of aboveground vegetation encourage the microflora, especially in the 

 surface horizons. Death of roots in the deeper soil provides a similar pos- 

 itive influence late in the season. At all but the highest bulk densities mi- 

 crofloral biomass is correlated with amounts of carbon present and 

 amounts of resin-extractable phosphorus. These factors establish some 

 upper value for potential biomass, while productivity is strongly gov- 

 erned by temperature. Temperatures do not differ sufficiently among mi- 

 crotopographic units to bring about the observed differences, which are 

 largely a product of moisture and aeration. Throughout the top 10 cm of 

 soil, moisture itself is seldom limiting to soil fungi, but insufficient oxy- 

 gen or excessive carbon dioxide is. High bulk densities and low oxygen 

 levels encourage bacteria over fungi, especially in deeper soil layers. The 

 anaerobic flora is capable of rapid decomposition within heated soils, 

 but under natural conditions the influences of impeded drainage and low 

 amounts of oxygen appear more profound than those of temperature. 



While relationships among mineral content, porosity, aeration and 

 moisture appear to modify the apparent "hospitality" of the organic 

 substrate available in some microtopographic units, the basins of low- 

 centered polygons remain an enigma. Physical measures suggest that ba- 

 sins should be favorable to microbes, but populations in standing dead 

 vegetation, litter and soil are consistently low. The high correlations be- 

 tween fungal abundance and resin-extractable phosphorus for basins, to- 

 gether with low amounts of phosphorus in basins, suggest a possible 

 chemical limitation. 



SUMMARY 



All components of the microflora of the coastal tundra at Barrow 

 are characterized by lower species diversity than is observed in other 

 Biomes, with the possible exception of some deserts. As in other Biomes, 

 algae (photosynthetic microorganisms) are best represented by green and 

 blue-green forms, which in the Biome research area contribute 42 of the 

 59 species identified. Several algal species are characteristic of fecally 

 contaminated environments, while others are planktonic, reflecting the 

 high amounts of moisture. Bacteria present in the system similarly reflect 

 the high amounts of moisture. Anaerobes, particularly facultative anaer- 

 obes, constitute 50 to 70% of the bacterial population and are important 



