Molecular Microbiology Research 2024, Vol.14, No.1, 49-60 http://microbescipublisher.com/index.php/mmr 51 3.3 Factors influencing the composition and activity of soil microbial communities Several factors influence the composition and activity of soil microbial communities, including plant species, soil type, and environmental conditions. Plant species and their associated root exudates significantly shape the microbial communities in the rhizosphere, the soil region influenced by root secretions. Soil type, including its pH, texture, and nutrient content, also plays a critical role in determining microbial community structure (Zhou et al., 2020a). Environmental factors such as moisture, temperature, and land management practices further modulate microbial activity and diversity (Paredes and Lebeis, 2016; Zhang et al., 2019). 4 Symbiotic Interactions Between Leguminous Plants and Soil Microbes 4.1 Types of symbiotic relationships between leguminous plants and soil microbes Leguminous plants engage in various symbiotic relationships with soil microbes, primarily with rhizobia and arbuscular mycorrhizal fungi (AMF). The rhizobia-legume symbiosis involves rhizobial bacteria forming nodules on the roots of leguminous plants, where they fix atmospheric nitrogen into a form usable by the plant (Oldroyd et al., 2011). Another significant symbiotic relationship is the tripartite symbiosis, where both AMF and rhizobia simultaneously associate with the same leguminous host, enhancing nutrient acquisition and plant growth in nutrient-deficient soils (Chang et al., 2017; Lace and Ott, 2018). 4.2 Mechanisms of symbiosis formation and maintenance The formation and maintenance of these symbiotic relationships involve complex molecular signaling and recognition processes. For rhizobia-legume symbiosis, the plant secretes flavonoids that trigger the production of Nod factors by rhizobia, which in turn initiate nodule formation on the plant roots (Oldroyd et al., 2011). Similarly, in AMF symbiosis, plants secrete strigolactones that activate mycorrhizal factors, facilitating the association with plant root hairs. The tripartite symbiosis requires coordinated gene regulation and mutual exchange of diffusible signal molecules to induce the expression of genes involved in the common symbiotic pathway (Chang et al., 2017; Lace and Ott, 2018). 4.3 Benefits of symbiosis for both plants and microbes The symbiotic relationships between leguminous plants and soil microbes are mutually beneficial. For the plants, these symbioses enhance nutrient acquisition, particularly nitrogen and phosphorus, which are critical for plant growth and productivity (Oldroyd et al., 2011; Shtark et al., 2012; Chang et al., 2017). Rhizobia fix atmospheric nitrogen into ammonia, which the plant can use, while AMF improve phosphorus uptake through their extensive hyphal networks (Shtark et al., 2012; Chang et al., 2017). In return, the microbes receive carbohydrates and other organic compounds from the plant, which serve as energy sources (Oldroyd et al., 2011; Chang et al., 2017). 4.4 Examples of legume-microbe symbioses The symbiotic relationship between leguminous plants and soil microorganisms is an important research field in plant ecology and agricultural production. These symbiotic relationships not only enhance plant nutrient absorption, but also play a crucial role in the global nitrogen cycle. The symbiotic relationship between rhizobia and soybean (Glycine max) is the most typical example. Rhizobia can form nodules in the roots of soybeans, fixing nitrogen in the atmosphere and converting it into a form that plants can utilize, thereby increasing soil fertility and reducing dependence on chemical nitrogen fertilizer (Ikeda et al., 2010). This symbiotic relationship is of great significance for improving agricultural productivity. The interaction between arbuscular mycorrhizal fungi (AMF) and peas (Pisum sativum) is another research focus. AMF helps plants more effectively absorb water and minerals, especially phosphorus, through symbiosis with pea roots. This symbiotic relationship not only enhances the growth and yield of peas, but also serves as an ideal model system for studying the mechanism of mycorrhizal symbiosis (Chang et al., 2017).
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