Molecular Microbiology Research 2024, Vol.14, No.1, 49-60 http://microbescipublisher.com/index.php/mmr 50 This review provides an overview of the current status of the interaction between leguminous plants and soil microorganisms, and discusses in detail the biological basis of the interaction and its variation under different environmental and management conditions through case analysis. Through a comprehensive review and analysis, this review aims to understand the practical significance of these interactions on ecosystems and agricultural production, and optimize their application in agriculture, providing support for future research and practice. 2 Leguminous Plants and Their Role in Nitrogen Fixation 2.1 Leguminous plants and their unique ability to fix atmospheric nitrogen Leguminous plants, belonging to the family Leguminosae (Fabaceae), are renowned for their unique ability to fix atmospheric nitrogen through a symbiotic relationship with nitrogen-fixing bacteria, primarily from the Rhizobium genus (Raza et al., 2020). This family is the third largest among angiosperms and includes a wide variety of forms ranging from annual herbs to large trees, distributed from tropical to arctic regions. The symbiotic relationship is facilitated by the formation of specialized structures called root nodules, where the bacteria reside and perform nitrogen fixation (Franche et al., 2009; Raza et al., 2020). 2.2 Mechanism of nitrogen fixation in leguminous plants The process of nitrogen fixation in leguminous plants involves a complex interaction between the plant roots and nitrogen-fixing bacteria. The bacteria infect the root hairs of the host plant, leading to the formation of root nodules. Inside these nodules, the bacteria differentiate into a form known as bacteroids, which are capable of converting atmospheric nitrogen (N2) into ammonia (NH3) through the action of the enzyme nitrogenase (Liu et al., 2018; Raza et al., 2020). The plant supplies the bacteria with carbohydrates derived from photosynthesis, which the bacteria use as an energy source for the nitrogen fixation process. This mutualistic relationship ensures that the fixed nitrogen is made available to the plant in a form that can be assimilated for growth and development (Liu et al., 2018). 2.3 Importance of nitrogen fixation for plant growth and soil fertility Nitrogen is a critical nutrient for plant growth, as it is a fundamental component of amino acids, proteins, and nucleic acids. However, atmospheric nitrogen is not directly accessible to most plants. The ability of leguminous plants to fix atmospheric nitrogen provides a significant advantage, allowing them to thrive in nitrogen-poor soils (Raza et al., 2020). This biological nitrogen fixation (BNF) not only supports the growth of the leguminous plants themselves but also enhances soil fertility by increasing the nitrogen content in the soil, benefiting subsequent crops planted in the same soil (Bhattacharjee et al., 2008; Patel, 2018; Raza et al., 2020). This process is environmentally friendly and sustainable, offering an alternative to chemical fertilizers, which can have detrimental effects on the environment. 3 Soil Microbial Communities 3.1 Types and functions of soil microbial communities Soil microbial communities are composed of a diverse array of microorganisms, including bacteria, fungi, archaea, and protozoa. These microorganisms play crucial roles in various soil processes. Bacteria and fungi are the most abundant and functionally diverse groups, with bacteria such as Proteobacteria, Actinobacteria, and Bacteroidetes being dominant in many soil environments (Zhou et al., 2020a). Fungi, particularly mycorrhizal fungi, are essential for plant nutrient uptake and soil structure formation (Schweitzer et al., 2008; Zhang et al., 2019). 3.2 Role of soil microbes in nutrient cycling, organic matter decomposition, and soil structure Soil microbes are integral to nutrient cycling, organic matter decomposition, and the maintenance of soil structure. They facilitate the breakdown of organic matter, releasing essential nutrients such as nitrogen, phosphorus, and potassium back into the soil, which are then available for plant uptake (Schlatter et al., 2015). Microbial mediation of niche differentiation in resource use is a key process, where different microbes access various nutrient pools, thus supporting plant nutrient partitioning. Additionally, soil microbes contribute to the formation and stabilization of soil aggregates, enhancing soil structure and porosity.
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