[Cir. 131— C] •■ 



CELLULOSE AS A SOURCE OF ENERGY FOR NITROGEr 



FIXATION/ 



By I. G. McBeth, Physiologist, Soil-Bacteriology and Plant- Nutrition Investigations. 



INTRODUCTION. 



The great chemical prmciple underlymg nitrogen fixation by 

 micro-organisms which was early msisted upon by Berthelot and 

 Winogradsky is that energy ui the form of organic carbon is neces- 

 sary for the fixation of gaseous nitrogen by the protoplasm of the 

 bacterial cell. Subsequent investigations have indicated that from 

 100 to 200 units of carbonaceous substance are utilized in the fixa- 

 tion of 1 unit of nitrogen; therefore, the quantity of carbonaceous 

 material m the soil becomes an exceedmgly important factor m 

 determining its nitiogen fixmg power. Within the last decade much 

 research has been undertaken to determine the kmd of carbonaceous 

 substances best adapted to serve as a source of energy for nitrogen- 

 fixing bacteria. These investigations have shown that a great num- 

 ber of compounds may be utilized either directly or mdii-ectly by 

 these organisms, but the nature of the compounds of greatest impor- 

 tance in the soil :'s still somewhat problematical. It seems certain, 

 however, that the source of energy for nitrogen fixation in soils must 

 be derived from the decomposing plant substances, and as by far 

 the larger part of the organic carbon added to the soil as roots, 

 stubble, etc., is in the form of cellulose, it would seem that this 

 substance may have a far reaching effect on the development of 

 nitrogen fixing organisms therein. 



As cellulose is sn inert compound inaccessible to such nitrogen- 

 fxing bacteria as Azotobacter it would seem that its value as a 

 source of energy for nitrogen fixation may, in a measure at least, be 

 dependent upon the activity of other organisms capable of breaking 

 it dowTi mto more accessible compounds. In studying the value of 

 these compounds as a source of energy for Azotobacter it seems 

 desirable to grow the ceUuluse destroying and nitrogen fixmg organ- 

 isms in association, or at least in the same nutrient solution. In 

 such an experiment it is obvious that the solution employed must be 

 favorable for the process of nitrogen fixation as well as for cellulose 

 destruction. 



» Issued July 5, 1913. 

 [Cir. 131] 



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