C H A l» I i: K 



I 6 



Decomposition of Complex Plant and 

 Animal Residues 



Actinomycetes are capable of attacking a 

 great variety of plant and animal products, 

 notalily crop residues; they thus bring about 

 the partial or complete decomposition of 

 these products. Actinomycetes may, there- 

 fore, be considered, on a par with the fungi 

 and the true bacteria, as one of the leading 

 groups of microorganisms concerned in the 

 destruction of organic materials and in trans- 

 formation and mineralization of organic mat- 

 ter in nature. The literature on the soil ac- 

 tinomycetes, beginning with the work of 

 Beijerinck, in the early days of the century, 

 and continuing through recent studies, 

 abounds in data on the abundance and ac- 

 tivities of actinomycetes in composts and in 

 soils rich in organic matter. The essential role 

 of these organisms in the formation and de- 

 composition of humus was early recognized. 

 These processes result in bringing about the 

 liberation of plant nutrients in available 

 forms and are thus of great importance in 

 plant nutrition and soil fertility. 



Decomposition of Plant Materials 



In a study of the decomposition of al- 

 falfa by different groups of microorganisms, 

 Waksman and Hutchings found that pure 

 cultures of actinomycetes were able to de- 

 compose, in 39 to 74 days, 33 to 43 per cent 

 of the hemicelluloses and 23.2 to 25.3 per 

 cent of the cellulose, as well as a part of the 

 lignin. Nearly 20 per cent of the total nitro- 



gen in the plant residues was liberated as 

 ammonia, thus pointing to considerable pro- 

 tein decomposition; much of the nitrogen 

 must also have been used by the organisms 

 for the synthesis of their own cell material. 

 In the decomposition of oat straw, 24.5 per 

 cent of the hemicelluloses were destroyed 

 in 50 days ; only little cellulose and some lig- 

 nin were attacked. Cornstalks were only 

 slightly attacked when no lime and phos- 

 phate were added but underwent rapid de- 

 composition when these were introduced. Of 

 the total dry plant material, the actinomy- 

 cetes brought about, on an average, 20 per 

 cent decomposition. They attacked the wa- 

 ter-soluble substances most readily (30.5 

 per cent), then the hemicelluloses (16.7 per 

 cent), and the cellulose least readily (5.4 

 per cent). The most striking point was the 

 fact that the actinomycetes decomposed not 

 only the cellulose and hemicelluloses, but 

 the lignin in these materials as well, even to 

 a greater extent than did the fungi, as il- 

 lustrated in Table 68. 



In a comparative study of the decomposi- 

 tion of cornstalks by several species of Strep- 

 tomyces, alone or in the presence of a fungus 

 or a bacterium, the streptomycetes were 

 highly effective in decomposing a consider- 

 able amount of the cellulose and the hemi- 

 celluloses. Although their decomposing ca- 

 pacity was less than that of the fungus Hu- 

 micola, especially in the absence of added 



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