Effectiveness of nitrogen fixation in rhizobia

Abstract

Summary Biological nitrogen fixation in rhizobia occurs primarily in root or stem nodules and is induced by the bacteria present in legume plants. This symbiotic process has fascinated researchers for over a century, and the positive effects of legumes on soils and their food and feed value have been recognized for thousands of years. Symbiotic nitrogen fixation uses solar energy to reduce the inert N 2 gas to ammonia at normal temperature and pressure, and is thus today, especially, important for sustainable food production. Increased productivity through improved effectiveness of the process is seen as a major research and development goal. The interaction between rhizobia and their legume hosts has thus been dissected at agronomic, plant physiological, microbiological and molecular levels to produce ample information about processes involved, but identification of major bottlenecks regarding efficiency of nitrogen fixation has proven to be complex. We review processes and results that contributed to the current understanding of this fascinating system, with focus on effectiveness of nitrogen fixation in rhizobia.

Response of Soil Bacterial Community Diversity and Composition to Time, Fertilization, and Plant Species in a Sub-Boreal Climate

“…The relative abundances of differential Flavobacteriales and Rhizobiales OTUs were higher in the red clover treatment than in the timothy treatment. Even though differences in absolute abundances cannot be concluded from differences in relative abundances (Gloor et al, 2017), it is likely that Rhizobiales abundances could have increased due to their capability to live in symbiosis with legumes (Lindström et al, 2019).…”

The symbiotic capacity of rhizobium shapes root-associated microbiomes

“…This interaction involves forming root or stem nodules in which rhizobia convert atmospheric nitrogen (N 2 ) into ammonia (NH 3 ) that is used as nitrogen-resource for the legume. In turn, legumes supply photosynthates to their bacterial symbionts [28,29]. Rhizobia-legume symbiosis is highly speci c and widely diverse [30,31].…”

Competition for electrons favors N2O reduction in denitrifyingBradyrhizobium isolates

“…Rhizobial inoculants are used since long to increase the yield of leguminous crops and at the same time avoid the need for synthetic fertilizers. Different combinations of rhizobial strain and legume cultivar may differ substantially in nitrogen fixation effectiveness, which is also affected by environmental conditions [15,68], and large efforts are put into the development of new inoculants that are compatible with various types of legumes as well as soil types and climates [69]. The present study shows that Bradyrhizobium strains also differ with respect to N2O reduction, and suggests that new inoculants should be selected among rhizobia that express Nos.…”