502 PRINCIPLES OF SOIL MICROBIOLOGY 



and microorganisms. As a result of the activities of microorganisms, 

 a large number of substances are formed from the decomposition of 

 proteins. The most important of these is ammonia. This is either 

 assimilated without change by plants or microorganisms or is first 

 converted into nitrates by the nitrifying bacteria. In addition to 

 ammonia, other nitrogenous compounds formed from the decomposi- 

 tion of proteins by microorganisms are beneficial to the growth of 

 higher plants. 81 It has even been suggested that substances such as 

 nucleic acid, hypoxanthine, guanine, histidine, arginine and creatinine, 

 are absorbed directly by the plant, without first being transformed into 

 ammonia and nitrates. Collectively these compounds were found to 

 be more beneficial than when used singly. 82 It is possible that these 

 substances, especially the nucleic acids, are not used as nutrients 

 directly, but play a role in the growth of plants and microorganisms 

 similar to that played by vitamines in the growth of higher plants. 



Some of the decomposition products may have a harmful effect 

 upon plant growth, 83 as in the case of the various nitrogenous and 

 non-nitrogenous substances that can be isolated from the soil, includ- 

 ing pyridine and its derivatives, dihydroxystearic acid, etc. 



Bacteria utilize a wide range of substances as sources of nitrogen, 

 including proteins and their derivatives which they tend to break 

 down further with the liberation of ammonia. 84 The same is true of 

 fungi. 85 According to Emmerling, fungi utilize the a-amino acids quite 



81 Schreiner, O., Reed, H. S., and Skinner, J. J. Certain organic constituents 

 of soils in relation to soil fertility. Bur. Soils, U. S. Dept. Agr. Bui. 47. 1909; 

 Schreiner, O., and Lathrop, E. C. The chemistry of steam heated soils. Jour. 

 Amer. Chem. Soc, 34: 1242-1259; Skinner, J. J. Effects of creatinine on growth 

 and absorption. Bur. Soils, U. S. Dept. of Agr. Bui. 83. 1911; Hutchinson, H. B., 

 and Miller, N. H. J. The direct assimilation of inorganic and organic forms of 

 nitrogen by higher plants. Centrbl. Bakt. II, 30: 513-547. 1911. 



82 Schreiner, O., and Skinner, J. J. Nitrogenous constituents and their bear- 

 ing on soil fertility. Bur. Soils, U. S. Dept. Agr. Bui. 87. 1912. 



83 Schreiner, O., and Shorey, E. C. 1909. The isolation of harmful organic 

 substances from soils. Bur. Soils, U. S. Dept. of Agr. Bui. 53. 1909; Chem- 

 ical nature of soil organic matter. Ibid., Bui. 74. 1910. 



84 Bierema, S. Die Assimilation von Ammon-Nitrat und Amidstickstoff 

 durch Mikroorganismen. Centrbl. Bakt. II, 23: 672-726. 1909; Nawiasky, P. 

 Ueber die Ernahrung einiger Spaltpilze in peptonhaltigen Nahrboden. Arch. 

 Hyg., 64: 33-61. 1908; Uber die Umsetzung von Aminosauren durch Bac. proteus 

 vulgaris. Arch. Hyg., 66: 209-243. 1908. 



86 Czapek, F. Untersuchungen iiber die Stickstoffgewinnung und Eiweiss- 

 bildung der Pflanzen. Beitr. Chem. Physiol. Path., 1: 538-560. 1902; 2: 557- 

 590. 1902; 3: 47-66. 1902; Emmerling, O. Aminosauren als Nahrstoff fur 



