Molecular Soil Biology 2024, Vol.15, No.3, 129-139 http://bioscipublisher.com/index.php/msb 132 provide a sustainable alternative to chemical fertilizers. Research indicates that effective management of Rhizobium-legume symbiosis can lead to reduced nitrogen fertilizer use, thereby lowering greenhouse gas emissions and energy consumption associated with fertilizer production (Abd-Alla et al., 2023). This not only benefits the environment but also reduces the input costs for farmers (Kebede, 2021). 3.3 Improvement of soil structure and microbial diversity Rhizobium bacteria contribute to the improvement of soil structure and the enhancement of microbial diversity. The formation of root nodules and the subsequent nitrogen fixation process can lead to better soil aggregation and stability. For example, the plantation of native legumes like Albizzia julibrissin has been shown to improve soil aggregate formation and enhance the microbial community structure in saline soils (Liu et al., 2021). This improved soil structure facilitates better water retention and root penetration, which are essential for healthy plant growth. Moreover, the presence of Rhizobiumand other beneficial microbes in the soil can create a more diverse and resilient microbial ecosystem, promoting overall soil health (AbdElgawad et al., 2020). 3.4 Contribution to sustainable agriculture and environmental health The integration of Rhizobium-legume symbiosis into agricultural practices is a key component of sustainable agriculture. By reducing the need for synthetic fertilizers and improving soil health, Rhizobium bacteria help create more sustainable farming systems. This approach not only enhances crop yields but also mitigates the environmental impact of agriculture. For instance, the use of biofertilizers like Rhizobium can lead to lower greenhouse gas emissions and reduced soil degradation, contributing to long-term environmental health (Yates et al., 2021b). Furthermore, the adoption of Rhizobium-based practices supports the development of eco-friendly and cost-effective agricultural systems, aligning with global efforts to promote sustainable food production. The role of Rhizobiumin legume nitrogen fixation offers numerous ecological and agricultural benefits, including enhanced soil nitrogen levels, reduced reliance on synthetic fertilizers, improved soil structure, and contributions to sustainable agriculture. These benefits underscore the importance of leveraging Rhizobium-legume symbiosis to boost soil health and promote environmentally sustainable farming practices. 4 Diversity of RhizobiumStrains 4.1 Taxonomy and classification of Rhizobiumspecies Rhizobium species are taxonomically diverse and are classified within the alpha and beta subclasses of the Proteobacteria. For instance, Mimosa pudica, a tropical invasive weed, has been found to associate with beta-rhizobia, including species within the Burkholderia and Cupriavidus genera. In New Caledonia, the majority of rhizobial strains isolated fromM. pudica belonged to Cupriavidus taiwanensis, with a few strains identified as Rhizobium mesoamericanum (Klonowska et al., 2012). This diversity highlights the broad taxonomic range of rhizobia and their ability to adapt to different legume hosts and environmental conditions. 4.2 Specific interactions between different legume species andRhizobiumstrains The interaction between specific legume species and Rhizobium strains can significantly influence nitrogen fixation and plant health (Jēkabsone et al., 2022). For example, in Vicia faba (faba bean), inoculation with specific Rhizobiumstrains such as NSFBR-12 and NSFBR-15 resulted in the highest nitrogen fixation and nutrient uptake, demonstrating the importance of selecting effective rhizobial strains for enhancing legume productivity (Allito et al., 2020). Additionally, Rhizobium leguminosarum bv. viciae strain 33504-Alex1 not only promoted growth in faba beans but also induced systemic resistance against Bean yellow mosaic virus, showcasing the multifaceted benefits of specific Rhizobium-legume interactions (Figure 2) (Abdelkhalek et al., 2022). The research of Abdelkhalek et al. (2022) illustrates the levels of various oxidative stress markers (SOD, CAT, APX, and PPO) in faba bean plants under different treatments, including control, Bean yellow mosaic virus (BYMV) infection, Rhizobiumsoil treatment, and foliar spray treatment. The results indicate that plants treated with Rhizobiumbefore BYMV inoculation (G3) show a significant increase in enzyme activities (SOD, APX, PPO) compared to other groups, suggesting enhanced antioxidant defense. In contrast, the control group (G1) generally exhibits lower levels of these enzymes, highlighting the stress-mitigating effect of the Rhizobiumtreatment.
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