The Microflora 281 



In the wet meadows, average seasonal abundance and productivity 

 of plateable bacteria in the surface soil were higher in 1971 than in 1973. 

 Because most of the increase in bacterial biomass occurs at the end of the 

 season, these observations suggest that the bacteria in the surface of the 

 soils were not encouraged by either the higher late season temperatures 

 or increased precipitation during 1973. The low temperatures en- 

 countered in deeper soil apparently did not suppress bacterial growth se- 

 verely. In 1971 direct counts gave an estimate of the minimal seasonal 

 bacterial productivity in wet meadow surface soils of about 1.2 g m"^ (1 

 cm)"' yr"' in the surface soil while the minimum productivity in the 

 deeper soil was 3.7 g m'^ (I cm)'' yr"'. Again it is possible that microbi- 

 vores, more active in surface soils, confuse these comparisons. 



ENVIRONMENTAL CONTROLS ON 

 MICROFLORAL BIOMASS 



Empirical spatial and temporal patterns are presented above. In the 

 following section, an attempt is made to account for the observed differ- 

 ences in microbial biomass among microtopographic units solely on the 

 basis of measured variables: organic substrate, inorganic nutrients, 

 temperature, moisture, and oxygen. The analysis is hmited to field data 

 for measured values from a number of different but natural environ- 

 ments. Soil fungi are the only group for which the data base is suffi- 

 ciently large to address specific relationships. 



Substrate 



If no other factors are acting, the soil microflora should increase as 

 the amount of organic substrate increases. The total amount of organic 

 material available to microorganisms was seldom measured directly. 

 However, the percentage organic carbon is strongly correlated with bulk 

 density (Chapter 7). Soils of higher bulk density contain more inorganic 

 matter and less organic substrate per gram of soil. Thus fungal density 

 should decline with increasing bulk density. For samples of all but the 

 lowest bulk densities, fungal density does decline with increasing bulk 

 density (Figure 8-10). Regression of fungal biomass in the surface soil (g 

 mycelia cm"') on amount of carbon per soil volume (g C cm"') suggests 

 that the response is associated with available substrate: 



fungal biomass = 0.633+0.014 (g C) {F = 12.47, n = 406). 



Thus, large differences in amounts of carbon on a volume basis are 



