Microflora Activities and Decomposition 303 



ary data suggest tiiat the fungal potential for hydrolysis of hemicellulose 

 resembles the pattern for utilization of pectin and starch. 



The response of the fungi thus contrasts directly with that of bac- 

 teria which apparently use less recalcitrant substrates preferentially as 

 temperature decreases. Widden (1977) made similar observations on 

 Devon Island. The byproducts of fungal cellulolysis may serve as sub- 

 strates for bacteria at temperatures below 5 °C and coevolution of inter- 

 dependent cold acclimations may result in closer relationships between 

 bacteria and fungi at lower temperatures. 



Our second hypothesis relates to the form of response with changing 

 temperature. Different enzymes produced by pure cultures of specific 

 tundra fungi have very different responses to temperature (Figure 9-5). 

 The low temperatures (< 10 °C) commonly encountered may encompass 

 simultaneously the optimal range for utilization of one substrate and the 

 unfavorable range for utilization of another. Flanagan and Scarborough 

 (1974) have shown that some cellulolytic fungi decompose cellulose opti- 

 mally below 10 °C, while in the same organism optimal amylase and pec- 

 tinase activity occurs above 30 °C. The pectinase activities of four fungal 

 isolates (Figure 9-5) have temperature optima between 18° and 30 °C, 

 while those for cellulase activities are between 6° and 14 °C. 



If such differences in enzyme activity through varying temperature 

 ranges occur in vivo, then the optimum temperature range for cellulose 

 decomposition in the field may be wider than for some other enzyme sys- 

 tems, e.g. pectinase and amylase. These observations help explain why 

 pectinolytic and amylolytic fungi are less frequently isolated or active at 

 low temperature than are cellulolytic forms (Figure 9-1). 



Literature on fungi from temperate regions often examines tempera- 

 ture as a regulator of fungal respiration, but relationships between tem- 

 perature and utilization of substrate have received less attention. Thus 

 both hypotheses presented here are not fully testable with regard to util- 

 ization of substrate. However, tundra fungi at Barrow do appear to ex- 

 tend their effective metabolic activity over a wide temperature range, by 

 incorporating different temperature optima for utilization of different 

 substrates. 



Temperature influences on microbial utilization of substrate, 

 growth and respiration seem to fall into three broad groups (Figures 9-2, 

 9-3 and 9-4). All three groups have a range of activity that extends below 

 0°C, while at the same time the population as a whole has the flexibility 

 to take advantage of mesic and higher temperatures. One group, includ- 

 ing several sterile soil fungi together with Mucor microsporus, shows 

 very gradual responses of growth and respiration to temperature values 

 in the range from -3 ° to +20°C. The second group shows a positive re- 

 sponse to increasing temperature up to an optimal point, but thereafter 

 shows no further response to increasing temperature in the range exam- 



