Microflora Activities and Decomposition 313 



TABLE 9-2 Parameter Values Giving the Best Fit of the gresp Func- 

 tion to Data from Seven Substrates and Coefficients of 

 Determination 



* rl is an estimate of the accountable variation explained by a nonlinear model. 



t An optimum solution was not found. 



NE — No estimate; number of measurements at moisture contents >500"7o moisture (% dry 



wt) are <10. Therefore 02/(^2 + A/) was set equal to 1. 

 Source: After Bunnell et al. 1977a. 



and accuracy of the model in predicting measured microbial respiration 

 from aboveground substrates, assessed visually (Figure 9-8) and statistic- 

 ally (Table 9-2), suggest that the hypothesis is applicable to a diversity of 

 aboveground substrates. 



Coefficients a^ and ai assess the moisture range over which mi- 

 crobial respiration is little affected by changes in moisture levels. The 

 range encompassed by these coefficients extends beyond the optimal 

 moisture regime determined for individual species, particularly at the up- 

 per end. Excluding the poorly constrained values (NE in Table 9-2) the 

 weighted mean of the mid-point between a, and ai for aboveground sub- 

 strates is 461% moisture on a dry weight basis. For the microbial com- 

 munity in toto, respiration from dead vegetation is depressed far more as 

 amounts of moisture approach the lower thresholds than near the upper 

 thresholds. Within plant litter where aquatic fungi are more abundant, 

 the upper limits to the moisture range may be greatly extended (Table 

 9-2; Flanagan and Veum 1974). 



Some substrates, particularly in taiga soils, have computed half- 

 saturation values that are equal for both a, and az (e.g. newly dead £"^0- 

 phorum angustifolium, Table 9-2). The resulting model with a, set equal 

 to 02 has only three parameters but accounts for 96°/o of the variation in 

 respiration from that substrate (Bunnell et al. 1977a). However, Bunnell 

 et al, (1977a) noted that equal values of a, and 02 are likely an artifact of 

 the model. Given the multiplicative form of the gresp function, a 



