234 PRINCIPLES OF SOIL MICROBIOLOGY 



Rdle of algae in the soil. It is impossible to generalize concerning the 

 role that algae may play in soil processes. Although it seems to be 

 definitely established that algae are unable to fix atmospheric nitrogen, 

 they may be able to do so by living symbiotically with nitrogen-fixing 

 bacteria. They may also accumulate organic matter in the soil, but 

 since they need available nitrogen, they may compete with higher plants 

 for the soluble minerals and available nitrogen compounds in the soil. 

 Gautier and Drouin 56 exposed samples of artificial soil, free from organic 

 material and containing only ammoniacal nitrogen, in a sheltered posi- 

 tion for a considerable period of time. The soil became, in course of 

 time, covered with algae (Pleurococcus vulgaris, Protococcus viridis, 

 etc.). This resulted in a loss in total nitrogen, a still greater loss in am- 

 monia nitrogen, and a gain in organic nitrogen. The ammonia nitrogen 

 was converted into organic nitrogen by the algae; with an increase in 

 growth, there was a decrease in the loss of the total nitrogen. The 

 algae thus play also a part in preventing the loss of ammonia nitrogen, 

 as well as the leaching out of nitrates from the soil. The probable 

 role of algae may thus consist in accumulating organic matter in newly 

 formed soils. 57 ' 58 It has been suggested 59 that algae, by taking in C0 2 

 and giving off oxygen, make swamp soils suitable for the growth of the 

 rice plant. The roots of rice plants are typical land roots and possess 

 no special adaptations to growth under swamp conditions. The large 

 supply of dissolved oxygen in the swamp water produced by the photo- 

 synthetic activity of the algae enables the rice plants to grow under 

 these artificial conditions. 60 



The fact that algae are present in the soil in considerable numbers, 

 that they can grow even in the subsoil and in the dark, that they re- 

 tain their vitality for very long periods, even after prolonged drought, 

 that they can store large quantities of energy thus making them avail- 

 able for other organisms, all point to their probable importance in 



66 Gautier, A., and Drouin, R. Recherches sur la fixation de l'azote par Ie sol 

 et les vegetaux. Compt. Rend. Acad. Sci. 106: 754-7, 863-6, 944-7, 1098-1101, 

 1174-6,1232-4. 1888;113:820-825. 1891. 



" Treub, M. Notice sur la nouvelle flore de Krakateu. Ann. Jard. Buiten- 

 zorg. 7: 213-223. 1888. 



" Fritsch, F. E. The role of algal growth in the colonization of new ground 

 and in the determination of scenery. Geogr. Jour. 30: 531-548. 1907. 



69 Harrison, W. H., and Aiyer, S. Gases of swamp rice soils. Pusa Mem., 

 Chem. Series, 3: 65-106. 1913; 4: 1-17. 1914. 



60 Brizi, U. Richerche sulla malattia del Rizo detta "Bruzone." Ann. dell 

 Instit. Agr. Dott, A. Buti. 5: 79-95. 1904;6:61-103. 1905;7:104-174. 1908. 



