286 



F. L. Bunnell et al. 



U 2000|-June 

 >> o 

 ■^ J 1500 



- o 1000 

 o .= 

 a< « 

 c u 



= ^ 5001- 





- July 



10 



^ 





- August 



I 



10 5 



Moisture Content, g water (gdw soil) 



in 



o 



CD <J 



CM 



<65 65-75 >75 «65 65-75 »75 <65 6575 »75 



Moisture Content, g water cm" soil 



FIGURE 8-14. The relationship of the density and 

 biomass of soil fungi to soil expressed on a dry weight 

 and on a volume basis for each summer month. (After 

 Laursen 1975.) 



growth declined in early July, apparently in response to declining mois- 

 ture. With increasing precipitation and moisture in August, rapid growth 

 resumed. Thus, in plant Utter, fungal density appears to be correlated 

 with moisture. 



In the highly organic soils the measured percentage of water by 

 weight is largely a function of the amount of inorganic material present 

 in the organic matrix. Estimates of fungal density per gram of soil show a 

 clear but somewhat misleading relationship with amounts of water per 

 gram of soil (Figure 8-14). As bulk densities and the amounts of in- 

 organic material increase, amounts of water per gram of soil decrease 

 and so does the relative amount of organic material available to support 

 microbial biomass and growth. 



Expressed on a volume basis, moisture content shows little variation 

 seasonally or with depth. Over the range of measures available, estimates 

 of fungal biomass per volume of substrate are generally highest for the 

 moisture class of 0.65 to 0.75 g water cm"' (Figure 8-14). Within this class 

 the percentage moisture on a weight basis ranges from less than 120% to 

 over 8(X)% moisture. Thus, when moisture contents are expressed on a 



