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PRINCIPLES OF SOIL MICROBIOLOGY 



actinomyces, which develop in the less acid aerated soils, also attack 

 the proteins readily, liberating ammonia even before all the carbohy- 

 drates have been decomposed, a process unimaginable for fungi. Bac- 

 teria leave a larger amount of the material in the form of intermediate 

 products, including the various organic acids. 



The extent of decomposition of carbohydrates by microorganisms 

 is found to depend not only on the nature of the organism, but also 

 on the nature and amount of available nitrogen. For every unit of 

 carbon decomposed as a source of energy, a certain amount of nitrogen 



Plant substances 



Aninfll substances 



Complex carbohydrates 



Proteins and other nitrogenous 

 substances 



Organic 



Free COo 



Fig. 55. Decomposition of organic matter in the soil by microorganisms 

 (original.) 



is assimilated, whether the latter is present in the form of proteins, 

 simple protein degradation products or inorganic salts. In this respect 

 the fungi differ distinctly from the bacteria. Fungi assimilate a great 

 deal of the carbon decomposed and, although their nitrogen requirement 

 is less than that of bacteria, the total amount of nitrogen assimilated is 

 much greater because of the comparatively much smaller amount of 

 protoplasm synthesized by the bacteria. 



A schematic presentation of the decomposition of carbohydrates and 

 proteins, the two most important constituents of natural organic matter, 

 with the formation of some intermediate and some final products is 



