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Abstract
Quantitative changes in bacterial, fungal and algal populations in the surface peat (0 to 5-cm depth) were studied during the spring thaw period at a tundra hummocky sedge-moss meadow (Devon Island, N.W.T., Canada). A significant peak in numbers of aerobic heterotrophic bacteria and in amounts of filamentous algae was observed during the thaw period. No significant maximum in fungal standing crop was evident during this period but an increase in the hyphae containing protoplasm after thaw was indicative of increased fungal activity. Data obtained at each sampling time were highly variable. This was probably due to the topographic heterogeneity of the site which gave rise to variation in soil moisture content and microenvironment.
Qualitative changes in bacterial populations were studied before and after thaw. Gram-negative psychotrophic types predominated and Bacillus spp. were rarely isolated. Certain Gram-negative groups, the fluorescent pseudomonads and the Cytophaga/Flexibacter types, were isolated less frequently after thaw while Gram-negative orange pigmented rods, Arthrobacter spp. and other coryneforms occurred more frequently after thaw.