Microflora Activities and Decomposition 299 



1973). Psychrophilic organisms are here defined as having a growth op- 

 timum at or below 20 °C (Griffin 1972). 



Temperature Influences on Microbial Growth and Respiration 



Metabolic processes of decomposers are generally adapted to the cold- 

 dominated environment. Respiration within soil and litter is measurable 

 down to -6.5 °C and substantial increases in fungal biomass have been 

 measured in soils when temperatures were between 0° and 2°C. Data on 

 growth and respiration of individual bacteria from the Biome research 

 area and other cold-dominated systems (Boyd 1967, Christensen 1974, 

 Mosser et al. 1976) have shown that strict psychrophiles are present, but 

 their incidence is less than 5 to 10% of the total plateable flora. 



Most fungi are cold-tolerant mesophiles able to respire heterotroph- 

 ically to -6.5 °C but with optima for growth and respiration between 20° 

 and 30 °C (Figure 9-2). Minimum and maximum temperatures at which 



250 



200 



» 150 



a> 



d 100 



o 



50- 



5.0 10.0 



15.0 20.0 25.0 



Temperoture, "C 



FIGURE 9-2. Influence of temperature on res- 

 piration of tundra fungi growing on potato ex- 

 tract in Gilson respirometers (1 m extract: 0.1 g 

 mycelium). M.s. - three different Mycelia ster- 

 ilia from Barrow tundra soil; C.h. = Clado- 

 sporium herbarum; M.m. = Mucor microspor- 

 us. Each point is a mean of three samples; six 

 readings per sample. Standard deviations ranged 

 from 5 to 7.5% of mean. (After Flanagan and 

 Scarborough 1974.) 



