Competition for legume nodule occupancy: a down-to-earth limitation on nitrogen fixation

Abstract

Management of the legume root nodule symbiosis can be constrained by inability to establish a specific bacterial symbiont in the nodules. Inoculant strains of rhizobia selected or engineered for improved nitrogen fixation ability usually do not achieve nodule occupancy in field soils that already contain active indigenous populations of rhizobia. Instead, some indigenous strain or strains, usually without remarkable nitrogen fixation potential, out-compete those in the inoculant for nodulation sites. Competition for nodule occupancy must be better understood in terms of its microbial ecology, biochemistry, and molecular biology.