The rhizosphere bacteria in grass-clover associations

Abstract

A quantitative and qualitative assessment was made of the rhizosphere populations of grass and of clover, growing together in soil, at different levels of nitrogen. The quantitative analysis showed less variation when the results were expressed as numbers of bacteria per gram of root than if they were expressed on a soil weight basis. On a root weight basis grass supported more bacteria than clover, and on a soil weight basis the converse held. The rhizosphere populations of clover and grass increased with increasing nitrogen supply. In the high nitrogen treatments the increase in numbers on grass was due to more vigorous growth, but the high number on the shaded clover plant was probably due to bacteria growing on decomposing root tissue. The qualitative analysis was made on bacterial isolates from the various rhizospheres and showed an abundance of branching bacteria. Only small differences were found between the isolates from clover and grass roots growing under the different conditions.