Molecular Microbiology Research 2024, Vol.14, No.2, 109-118 http://microbescipublisher.com/index.php/mmr 109 Feature Review Open Access Symbiotic Nitrogen Fixation: The Role of Rhizobia in Enhancing Legume Growth and Soil Fertility Yunxia Chen, Xinhua Zhou Tropical Legume Research Center, Hainan Institute of Tropical Agricultural Resources, Sanya, 572025, Hainan, China Corresponding author: xinhua.zhou@hitar.org Molecular Microbiology Research, 2024, Vol.14, No.2 doi: 10.5376/mmr.2024.14.0012 Received: 07 Mar., 2024 Accepted: 16 Apr., 2024 Published: 28 Apr., 2024 Copyright © 2024 Chen and Zhou, This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Preferred citation for this article: Chen Y.X., and Zhou X.H., 2024, Symbiotic nitrogen fixation: the role of rhizobia in enhancing legume growth and soil fertility, Molecular Microbiology Research, 14(2): 109-118 (doi: 10.5376/mmr.2024.14.0012) Abstract Symbiotic nitrogen fixation, facilitated by rhizobia, plays a crucial role in enhancing legume growth and soil fertility. This symbiotic relationship has evolved to allow rhizobia to fix atmospheric nitrogen into a form usable by plants, significantly impacting agricultural productivity and ecological sustainability. This study summarizes the current understanding of the mechanisms, effectiveness, and ecological implications of rhizobia-legume symbiosis in nitrogen fixation. The study found that the effectiveness of nitrogen fixation varies significantly among different rhizobial strains, with some strains demonstrating high efficiency under specific conditions. The interaction between plant nitrogen demand and symbiotic efficiency is tightly regulated by systemic signaling pathways. Reactive oxygen and nitrogen species play a dual role in both promoting and regulating the symbiotic process. Environmental factors such as soil nitrate levels and herbivory also influence the allocation of fixed nitrogen in legumes. The rapid evolution of rhizobial strains through lateral gene transfer may lead to the emergence of competitive but less efficient nitrogen-fixing strains. Understanding the complexity and adaptability of the rhizobia-legume symbiosis can inform strategies to enhance nitrogen fixation efficiency, thereby improving legume growth and soil fertility. Future research should focus on unraveling the specific regulatory mechanisms and environmental interactions that optimize this symbiotic relationship. Keywords Symbiotic nitrogen fixation; Rhizobia; Legumes; Soil fertility; Molecular mechanisms; Ecological impact 1 Introduction Symbiotic nitrogen fixation is a critical biological process where atmospheric nitrogen (N2) is converted into ammonia (NH3) by symbiotic bacteria, primarily rhizobia, within the root nodules of leguminous plants (Sindhu et al., 2019). This process is essential for plant growth and soil fertility, as it provides a natural and sustainable source of nitrogen, a key nutrient for plant development (Liu et al., 2018a). The resulting symbiosis not only enhances the growth and productivity of legume crops but also contributes to improving soil fertility by increasing nitrogen content in the soil. Rhizobia have evolved a dual lifestyle, alternating between a free-living phase in the soil and an intracellular symbiotic phase within legume root nodules, which has allowed them to spread across diverse ecological niches and persist through evolutionary history (Masson-Boivin and Sachs, 2018). As global agriculture faces the challenges of increasing food demand, reducing environmental impact, and maintaining soil health, understanding and harnessing the benefits of symbiotic nitrogen fixation has become increasingly vital. Rhizobia play a pivotal role in agriculture by enhancing the growth and productivity of leguminous crops, which are vital for food security and soil health. The symbiotic relationship between rhizobia and legumes not only boosts plant growth by providing essential nitrogen but also improves soil fertility, reducing the need for chemical fertilizers (Lindström and Mousavi, 2019). This mutualistic interaction is tightly regulated by the host plant, ensuring efficient nitrogen fixation and optimal plant health (Oldroyd et al., 2011). Additionally, rhizobia-mediated nitrogen fixation has been shown to enhance plant defense mechanisms against herbivores, further contributing to the overall fitness and resilience of leguminous plants (Thamer et al., 2011). The ability of rhizobia to adapt and evolve in response to environmental conditions and host plant requirements underscores their significance in sustainable agricultural practices (Nandasena et al., 2007).
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