ON THE ROLE OF SOIL BACTERIA IN PLANT NUTRITION

Abstract

1. Soil microorganisms play an important role in plant nutrition. Many species of microbes, especially those that abundantly develop in the rhizosphere, exert a direct influence on plant nutrition. These microbes synthesize various biologically very active organic compounds and transmit them to the plants. The latter absorb through their roots the microbial metabolites and use them as sources of additional nourishment.2. The present paper shows that some bacteria aid in the accumulation of amino acids in plant tissues. In the presence of certain species of activating bacteria the amount of amino acids in the plant tissues increases 50-100 per cent or more. In leguminous plants more amino acids are accumulated under the influence of active nodule bacteria. As a rule, the more nodules on the roots, the more free amino acids in the tissues. Greater concentration of amino acids is also observed under the influence of certain non-nodule bacteria-Bacterium sp., Ps. fluorescens, etc.. A particularly high increase in amino acids in leguminous plants is observed when they grow in the presence of Ps. fluorescens.3. A similar effect is produced by certain activating bacteria on non-leguminous plants. The tissues of cereals (maize, wheat, barley, etc.) also show an increased accumulation of free amino acids in the presence of bacteria although to a lesser extent than those of the leguminous plants.4. Certain activating bacteria influence the acumulation of phosphorus containing organic compounds in plant tissues. These compounds are in some extent synthesized by bacteria and are transmitted to the plants through the roots. This was shown in the experiments with tracer phosphorus P32 with the simultaneous use of the method of paper chromatography.