262 Associative and Antagonistic Effects 



59,666 organisms per gram, with only 0.61 per cent actinomycetes 

 and 0.27 per cent fungi. These organisms, even in such low num- 

 bers, were found to be made up of various distinct types, as brought 

 out by differences in pigmentation, staining reactions, and spore for- 

 mation. The limited quantity of nutrients brought in by subter- 

 ranean drainage or rainfall, by localized growth of a plant or an 

 animal, will result in formation and liberation of small amounts of 

 nutrients for keeping the microbial population alive. The organisms 

 capable of living in this environment find comparatively little com- 

 petition. 



Table 58. Influence of Growing Plants on Number of 

 Microorganisms in Soil (from Starkey) 



Microorganisms Found * 



Among these organisms, the autotrophic bacteria are of prime im- 

 portance. These are highly specialized forms, capable of using as 

 sources of energy the traces of ammonia brought down by the rain 

 or the traces of hydrogen and methane found in the atmosphere. 

 Although very little fixed nitrogen is available to the autotrophic 

 bacteria, the traces produced by atmospheric discharges and brought 

 down by the rainfall will suffice, since energy is the all-important 

 limiting factor, and nitrogen-fixing bacteria are hardly able to exist 

 under these conditions until specialized higher plants become estab- 

 lished or complex forms of energy are made available. Microbial 

 life is thus at a minimum under these conditions and competition is 

 limited, since the carbon source required for cell synthesis, COu>, is 

 all-abundant. Only upon death of the microorganisms, when they 

 become themselves nutrients for other organisms, does competition 

 set in. A certain amount of association is possible, as when nitrate- 



