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



TABLE 9-4 Measured and Simulated Chemical Composition 



After One Year and Rates of Weight Loss of Erio- 

 phorum angustifolium Standing Dead Material 



♦Measured values use changes in identified age classes. 

 tSimulated values used abiotic data from 1973. 

 Source: Bunnell et al. (1977b). 



where /:, is the computed daily rate of weight loss due to respiration. The 

 three equations above make up the model decomp. Using meteorological 

 data from the Barrow site, Bunnell et al. (1977b) computed daily values 

 of the function gresp as determined by temperature and moisture and 

 applied these to the chemical-specific coefficients. They obtained annual 

 rates of weight loss of -0.66 and -0.13 for ethanol-soluble and ethanol- 

 insoluble constituents respectively. Measured weight losses from the total 

 litter in the field are -0.69 and -0.12 g g"' yr"'. The rates of weight loss 

 computed from temperature-moisture-chemical-specific rates of respira- 

 tion are thus in very close agreement with measured rates of weight loss. 

 Because the loss rates are chemical-specific (Bunnell et al. 1977b), the 

 model decomp can project not only total substrate weight loss but also 

 chemical composition, which is also very similar to the observed value 

 (Table 9-4). 



The model DECOMP provides a framework that permits extrapola- 

 tion of laboratory measures of microbial activity to predict total loss of 

 substrate weight and changing composition of substrate. The concepts of 

 decomposition embodied in the model appear supported by combined lab- 

 oratory and field evidence. The reasonably close agreement between sim- 

 ulated and measured values for standing dead material (Table 9-4) sug- 

 gests that at least during the initial period of decomposition many of the 

 changes in substrate weight and chemical composition result from chang- 

 ing rates of microbial respiration which are chemical-specific and inde- 

 pendently influenced by temperature and moisture (Bunnell et al. 1977b). 



