Diversity of Rhizobia and Importance of Their Interactions with Legume Trees for Feasibility and Sustainability of the Tropical Agrosystems

Emanoel G Moura,Juliana L B Souza,Cassia P C Bucher,Carlos A Bucher,Altamiro S L Ferraz Junior,Cristina S Carvalho,Alana C F Aguiar,Katia P Coelho

doi:10.3390/d12050206

Abstract

Symbiotic biological nitrogen fixation (BNF) is a complex process that involves rhizobia, a diverse group of α and β-proteobacteria bacteria, and legume species. Benefits provided by BNF associated with legume trees in tropical environments include improvements to efficiency of nitrogen (N) use, increase of soil carbon sequestration, stabilization of soil organic matter, decrease of soil penetration resistance, and improvement of soil fertility. All these benefits make BNF a crucial ecosystem service to the sustainability of tropical agriculture. Due to the importance of this ecological process and the high diversity of rhizobia, these bacteria have been extensively characterized worldwide. Currently, over 400 species of rhizobia are known, distributed into seven families. In the humid tropics, Leucaena leucocephala, Acacia mangium, Gliricidia sepium, and Clitoria fairchildiana are four of the most common species used by family farmers to create sustainable agricultural systems. These four legumes perform symbiosis with different groups of rhizobia. Exploring BNF could help to enable sustainable intensification of agriculture in the humid tropics, mainly because it can increase N use efficiency in an environment where N is a limiting factor to plant growth.

Highlights

Rhizobia Strains and Legume Tree InteractionsThe edaphoclimatic conditions, which involve soils with fragile structure subjected to high temperatures, rainfall, and insolation, are unfavorable for organic matter accumulation and N availability and nitrogen use efficiency
No-tillage alley cropping can be an alternative for the family farmers for maintaining productivity in the low-fertility soils of humid tropical regions
Nitrogen (N) fixation by legume trees, in which bacteria living in root nodules convert atmospheric dinitrogen (N2 ) gas to a plant-available form of N, is crucial to the sustainability of tropical agriculture [6]

Summary

Rhizobia Strains and Legume Tree Interactions

The edaphoclimatic conditions, which involve soils with fragile structure subjected to high temperatures, rainfall, and insolation, are unfavorable for organic matter accumulation and N availability and nitrogen use efficiency. Following the work of Fischer et al [5], we define ecosystem services as the ecological processes of ecosystems that are used to produce human well-being In this context, nitrogen (N) fixation by legume trees, in which bacteria living in root nodules convert atmospheric dinitrogen (N2 ) gas to a plant-available form of N, is crucial to the sustainability of tropical agriculture [6]. Species-specific legume–rhizobial interactions can directly influence niche and fitness differences among legume species and between legumes and non-legumes, with important consequences for the richness–productivity relationship [45] Both the rhizobia–host specificity and the diversity of the native rhizobia community are fundamental for the efficient use of inoculants. This occurs with the inoculation of beans in Latin American agricultural fields [49]

Identification of Bacterial Strains and Determination of Rhizobia Diversity

Diversity of Rhizobia in Nodules of Legume Trees in the Humid Tropics

Findings

Final Considerations