Enhancing Rhizobium–Legume Symbiosis and Reducing Nitrogen Fertilizer Use Are Potential Options for Mitigating Climate Change

Abstract

This review article explores the impact of nitrogen fertilizers on the symbiotic relationship between Rhizobium bacteria and legume plants. Nitrogen fixation has the potential to address the global protein shortage by increasing nitrogen supply in agriculture. However, the excessive use of synthetic fertilizers has led to environmental consequences and high energy consumption. To promote sustainable agriculture, alternative approaches such as biofertilizers that utilize biological nitrogen fixation have been introduced to minimize ecological impact. Understanding the process of biological nitrogen fixation, where certain bacteria convert atmospheric nitrogen into ammonia, is crucial for sustainable agriculture. This knowledge helps reduce reliance on synthetic fertilizers and maintain soil fertility. The symbiotic relationship between Rhizobium bacteria and leguminous plants plays a vital role in sustainable agriculture by facilitating access to atmospheric nitrogen, improving soil fertility, and reducing the need for chemical fertilizers. To achieve optimal nitrogen fixation and plant growth, it is important to effectively manage nitrogen availability, soil conditions, and environmental stressors. Excessive nitrogen fertilization can negatively affect the symbiotic association between plants and rhizobia, resulting in reduced soil health, altered mutualistic relationships, and environmental concerns. Various techniques can be employed to enhance symbiotic efficiency by manipulating chemotaxis, which is the ability of rhizobia to move towards plant roots. Plant-specific metabolites called (iso)flavonoids play a crucial role in signaling and communication between legume plants and rhizobia bacteria, initiating the symbiotic relationship and enhancing nitrogen fixation and plant growth. Excessive nitrogen fertilizer application can disrupt the communication between rhizobia and legumes, impacting chemotaxis, root exudation patterns, nodulation, and the symbiotic relationship. High levels of nitrogen fertilizers can inhibit nitrogenase, a critical enzyme for plant growth, leading to reduced nitrogenase activity. Additionally, excessive nitrogen can compromise the energy demands of nitrogen fixation, resulting in decreased nitrogenase activity. This review discusses the disadvantages of using nitrogenous fertilizers and the role of symbiotic biological nitrogen fixation in reducing the need for these fertilizers. By using effective rhizobial strains with compatible legume cultivars, not only can the amounts of nitrogenous fertilizers be reduced, but also the energy inputs and greenhouse gas emissions associated with their manufacturing and application. This approach offers benefits in terms of reducing greenhouse gas emissions and saving energy. In conclusion, this paper provides a comprehensive overview of the current understanding of the impact of nitrogen fertilizers on the symbiotic relationship between Rhizobium and legume plants. It also discusses potential strategies for sustainable agricultural practices. By managing nitrogen fertilizers carefully and improving our understanding of the symbiotic relationship, we can contribute to sustainable agriculture and minimize environmental impact.

Impact of Plant–Microbe Interactions with a Focus on Poorly Investigated Urban Ecosystems—A Review

“…Nitrogen fixation in legumes has considerable ecological, agronomic, and environmental impacts. It is estimated that the biological nitrogen fixation process leads to the release of 52-130 million tons of nitrogen per year globally, with a significant reduction in the use of potentially harmful chemical fertilizers [73]. Due to their unique metabolic capabilities, PGPR are also of great interest in the bioremediation field, where rhizobacterial species able to sequester toxic heavy metals and degrade xenobiotic compounds may be used in association with plants to decontaminate polluted soils [50][51][52]72,74].…”

Unlocking the Potential of Inoculation with Bradyrhizobium for Enhanced Growth and Symbiotic Responses in Soybean Varieties under Controlled Conditions

“…Consequently, biological nitrogen fixation (BNF), a process in which atmospheric nitrogen is converted into organic forms by symbiotic and symbiotic microorganisms in the soil [21], has garnered significant attention. Symbiotic nitrogen fixation proves most beneficial for leguminous crops [22]. However, a specific relationship exists between the rhizobial strain and the plant varieties, necessitating compatibility for successful nodulation and nitrogen contribution [23].…”

Reinoculation in Topdressing of Rhizobium tropici, Azospirillum brasilense, and the Micronutrients Mo/Co in Common Bean

“…The plant receives nitrogen fixed by the microsymbiont rhizobium in ammoniacal form, assimilating it into nitrogenous compounds that can be translocated to its different parts [14]. The leguminous plants develop by symbiotic association in the roots with the rhizobial bacteria, and when these bacteria are present in the soil, naturally or via inoculation, they recognize and infect the roots of the host plant, causing the formation of nodules where the biological fixation of N 2 occurs [15,16].…”