298 P. W. Flanagan and F. L. Bunnell 



or soil. The potential for decomposition of pectin is lower in the phyllo- 

 sphere than in litter while the opposite is true in the case of potential 

 amylase activities. Both the phyllosphere and litter contain more utilizers 

 of pectin and starch than do soils. This pattern is the reverse of the trend 

 in distribution of utilizers of lignocellulose. In summary, a trend of in- 

 creasing ability to degrade larger molecules is apparent proceeding from 

 the phyllosphere into the soil. 



ABIOTIC VARIABLES AND MICROFLORA ACTIVITIES 



Despite the low annual input of energy to tundra, the active layer of 

 the soils is rich in carbon (9 to 20 kg m"^ to 20 cm depth) and contains 

 much energy. The energy contents of wet meadow soils range from 13.8 

 kJ (gdw soil)"' in the 0- to 2-cm horizon to 9.6 kJ (gdw soil)"' at depths of 

 12 to 18 cm. These resources of carbon and energy could sustain substan- 

 tial microbial production, provided other environmental conditions were 

 satisfactory. Potentially limiting factors include low temperatures and 

 reduced availability of moisture, oxygen and inorganic nutrients. 



Here we treat two themes: 1) potentially adaptive responses to low 

 temperatures, and 2) relationships between measured soil oxygen, associ- 

 ated moisture levels, and activities of microbial groups. 



Responses to Temperature 



Temperature influences microbial activity in at least three ways. 

 Both growth rates and respiration rates of microorganisms are affected 

 as well as the activities of specific enzymes used to degrade substrates. 

 Cardinal influences of temperature on organisms and their enzymes de- 

 termine the upper and lower tem.perature thresholds. The form of the re- 

 sponse may differ between cardinal points. We have examined the influ- 

 ence of temperature on tundra microorganisms within the framework of 

 two broad hypotheses: 



1) Tundra microorganisms gain cold tolerance by extending their 

 range of metabohsm towards lower temperatures. 



2) Tundra microorganisms enhance their effective metabolic range 

 by showing linear rather than exponential responses to low 

 temperature (Bunnell et al. 1977a). 



The first hypothesis addresses the depression of the lower cardinal tem- 

 perature; the second addresses the form of response to changing temper- 

 ature. Both hypotheses relate to psychrophily. Definitions of psychro- 

 phily and mesophily vary (Ingraham 1958, Griffin 1972, Christophersen 



