Microflora Activities and Decomposition 327 



teria which cannot degrade compounds of larger molecular weight. De- 

 composition of such compounds remains poorly understood, but it ap- 

 pears that accumulation of organic matter in tundra is more a product of 

 high moisture levels than of low temperatures. 



Microbes and Turnover of Organic Matter and Nutrients 



The preceding models concentrate on rates of microbial activity and 

 ignore microbial biomass. The accuracy of the predictions made by these 

 models suggests that concentration on rates of processes is an insightful 

 approach. That in no way obviates attempts to examine the consistency 

 of the measures of microbial biomass with estimated turnover of organic 

 matter. Growth, respiration, production efficiency, and maintenance 

 demands of the microbial biomass in specific substrates can be related to 

 weight loss from that substrate. Using the chemostat model of Marr et al. 

 (1963) it is possible to examine compatibility between field and labora- 

 tory data and to evaluate the influence of microbial activities on turnover 

 and accumulation of organic matter. Several workers (Babiuk and Paul 

 1970, Gray and Williams 1971, Flanagan and Bunnell 1976) have used 

 this approach in attempting to balance budgets of energy or carbon in a 

 variety of ecosystems. The biomass equation of Marr et al. (1963) is ex- 

 pressed as: 



idx/dt) + ax = Y(ds/dt) 



where x = microbial biomass 



5 = substrate available for microbial growth 



Y - yield coefficient, g microbial tissue (g substrate)"' 



a = specific maintenance rate — g microbial tissue required to 



maintain 1.0 g microbial tissue for a specific time, e.g. 1.0 



hour. 



When the rate of growth is zero, the above can be expressed: 



ds/dt = ax/Y'. 



The yield coefficient Y' is not identical to y because at zero growth there 

 is no actual yield. However, material for maintenance is believed to be 

 utilized at very nearly the same level of efficiency as material assimilated 

 for production of new tissue. 



Gray and Williams (1971), following the approach of Babiuk and 

 Paul (1970), utilized values for Y' anda of 0.3 g g"' and 0.001 g g' hr"' 

 respectively. Their values for x and a were derived from field data col- 



