Elevated populations of effective rhizobia in the rhizoplane of white clover growing in pasture

Abstract

Rhizobium populations were counted in random soil samples from a ryegrass/clover pasture, in soil around white clover plants, and also in the rhizoplane of the white clover roots. The random soil samples contained 3 × 105 cells per g dry soil of Rhizobium leguminosarum bv. trifolii effective on its host, and the same number of Mesorhizobium loti. Soil around white clover plants had 106 cells per g dry soil of each Rhizobium. In the rhizoplane of white clover there were 106 effective R. leguminosarum bv. trifolii per mg root dry weight, and only 103M. loti per mg root dry weight. The increase in the ratio of effective white clover rhizobia to M. loti in the rhizoplane demonstrates species-specific stimulation of effective rhizobia on the root surface. This would be important for the ongoing cycles of effective nodulation required by the clonal growth habit of white clover in pasture. © 2006 Taylor & Francis Group, LLC.