TRANSFORMATION OF MINERALS IN THE SOIL 645 



the metabolism of all microorganisms. Large quantities of these are 

 taken from the soil solution and synthesized into microbial protoplasm. 

 Notwithstanding the fact that in the decomposition of plant residues and 

 animal manures, phosphates and potassium salts are quite soluble, Kraw- 

 kow 2 found that when organic matter is decomposed in the soil by mi- 

 croorganisms, calcium and magnesium are less soluble. The decomposi- 

 tion and synthesis of organic matter in the soil takes place constantly 

 and leads to constant changes in the amount of available minerals in 

 the soil. It has been suggested 3 that fungi take a more active part in 

 the decomposition of mineral soil constituents than root secretions of 

 higher plants. A great many bacteria also play important roles in 

 the process. The fungi and algae as well as other groups of micro- 

 organisms store away considerable quantities of soluble minerals in 

 the form of microbial protoplasm due to the extensive growth of the 

 organisms in the presence of available energy. 4 



Decomposition of rocks and rock constituents by microorganisms. Not 

 only the mineral constituents of normal soils but rocks as well may 

 undergo disintegration and degradation through the action of micro- 

 organisms. Autotrophic bacteria obtain their carbon from the carbon 

 dioxide of the atmosphere and their energy from inorganic substances 

 of the soil or ammonia formed by electrical discharges and rainfall; 

 algae utilize the photosynthetic energy of the sun. The various inor- 

 ganic and organic acids formed by these organisms exert solvent action 

 upon the rocks. 



The chemosynthetic assimilation of C0 2 , fixation of nitrogen, and 

 denitrification are considered 5 as the three most primitive activities 

 of microorganisms in the development of life upon this planet. It 

 has been demonstrated 6 that various algae, particularly the Cyanophy- 

 ceae, exert a corroding effect upon stones. Diatoms transform alumi- 



2 Krawkow, S. The processes of interaction of the soluble products of decom- 

 position of organic matter with the soil constituents. Zhur. Opit. Agron., 9: 

 569-624. 1908; 10: 1-34. 1909. 



3 Kunze, F. Tiber Sauereausscheidung bei Wurzeln und Pilzhyphen und 

 ihre Bedeutung. Jahrb. wiss. Bot., 42: 357-391. 1906. 



4 Pantanelli, 1915 (p. 633). 



6 Fischer, II . Physiologische Leistungen primitivster Organismen in ihrer 

 stammesgeschichtlichen Bedeutung. Centrbl. Bakt. II, 55: 1-5. 1921. 



6 Jensen, P. R. Uber Steinkorrosion an den Ufern von Fureso. Intern. 

 Rev. ges. Hydrob. Hydrogr. Leipzig, 2. 1909; Roux, M. Recherches biologiques 

 sur le lac d'Annecy. Ann. biol. lacustre., 2. 1907. 



