MORPHOLOGICAL AND PHYSIOLOGICAL GROUPS OF SOIL BACTERIA FROM THE ROOTS OF BARLEY AND OATS

Abstract

Morphological and physiological characteristics were studied of more than 2400 stock-cultures of bacteria isolated from rhizosphere soils of barley and oats, and from control soils. Gram-positive rods were proportionately more numerous in control soils than in rhizosphere soils; this difference was greater with oats than with barley. The proportion of Gram-negative rods was greater in rhizosphere soils than in controls but not more so for one crop than the other. Gram-positive rods replaced a significant portion of Gram-negative rods in soils of the mature barley plants. The only significant increase in percentage incidence of physiological groups in rhizosphere soils was in regard to nitrate-reducing bacteria of the young oats plants. On the other hand there were significantly smaller percentages for starch-hydrolyzing bacteria and gelatin liquefiers in oats rhizospheres than in the controls. There were not any significant differences between rhizospheres and controls with regard to physiological groups from the barley plants. It is concluded that the proportional incidences of some physiological groups of soil bacteria are not greatly increased, but in some instances are decreased, by the presence of barley or oat roots growing in Chicot sandy loam.