The Microflora 257 



TAXONOMIC STRUCTURE: ITS GENERAL 

 CHARACTER AND HETEROGENEITY 



Bacteria and Actinomycetes 



Fewer species of bacteria are observed in tundra soils than in soils of 

 the temperate zone, while actinomycetes are sharply reduced or entirely 

 absent, presumably because of the acid, organic nature of the soils. 

 Among tundra areas, greatest densities of actinomycetes relative to total 

 bacterial populations have been reported from drier, less acid areas 

 (Kriss 1947, Widden 1977). The dominant bacteria isolated from a wide 

 variety of microtopographic units in the tundra at Barrow were gram 

 negative short rods. In wet meadows Pseudomonas, Achromobacter and 

 Flavobacterium were the most frequent genera. In drier areas, where 

 polygonal terrain predominated, three species of Achromobacter along 

 with Cytophaga hutchinsonii were most frequent. The dominance of 

 these bacterial groups agrees with earlier reports by Soviet researchers 

 working with northern soils (Mishustin and Mirzoeva 1972) and the re- 

 view of Dunican and Rosswall (1974) of studies in arctic and antarctic 

 tundra. The presence of Cytophaga at both wet and dry sites suggests 

 that the potential for cellulose decomposition by bacteria is widespread 

 in tundra. 



Numbers of gram positive bacteria, including spore-forming bacter- 

 ia that are largely gram positive, were generally less than 10' gdw"' soil at 

 the Biome research area. The low numbers are in agreement with find- 

 ings from most other high latitude sites (Boyd et al. 1966, Fournelle 

 1967, Dunican and Rosswall 1974). Some genera, such as Arthrobacter 

 and Bacillus, were isolated primarily from drier areas with polygonal ter- 

 rain. In the wet meadow Arthrobacter had a frequency of occurrence of 

 less than S'Vo, increasing in late season to 10% of the plateable flora. 

 Corynebacterium (C equi, C. sepedonicum and C. pseudolipheucium) 

 isolated from polygonal terrain are reported from only one other tundra 

 location (Truelove Lowland, Widden 1977). 



The work of Nelson (1977) suggests some possible reasons for the 

 relative frequency of Pseudomonas, Arthrobacter and Bacillus. She 

 found Pseudomonas spp. to be very resistant to starvation stress, which 

 is a possible adaptation to the low amounts of some soil nutrients. Ar- 

 throbacter spp. were tolerant of freezing and thawing effects when in- 

 oculated into sterile soil, while Bacillus spp., which are less commonly 

 encountered, were more sensitive to both stresses under the conditions 

 studied and less tolerant of low temperatures. 



