Legume Genomics and Genetics 2025, Vol.16, No.3, 108-127 http://cropscipublisher.com/index.php/lgg 117 Another potential of the legume-microorganism symbiotic system in biological control is the "barrier" effect of directly inhibiting soil-borne pathogens. Some members of the legume symbiotic microbial community have the ability to antagonize pathogenic microorganisms. For example, Bacillus colonized in the rhizosphere can produce antibiotics such as lichenin to inhibit the reproduction of fungal pathogens; Pseudomonas can compete for iron ions, carbon sources, etc., and take away the survival resources of pathogens. These effects can reduce the number of pathogens in the rhizosphere of legumes, thereby reducing the chance of infection. The luxuriant root system and large amount of mucus produced by legumes due to symbiosis also physically form a rhizosphere microenvironment dominated by beneficial bacteria, which is not conducive to the colonization of pathogens. Xu et al. (2021) found that the number of beneficial actinomycetes and actinomycetes in the soil of orchards planted with leguminous green manure increased, while the number of soil-borne pathogenic fungi such as Fusarium and Fusarium decreased, thereby reducing the incidence of root diseases in fruit trees. It can be seen that the legume symbiotic system can inhibit and prevent diseases by changing the structure of the rhizosphere microbial community. 5 Ecological Benefits of Legume-Microbe Symbiosis 5.1 Reducing chemical fertilizer use and greenhouse gas emissions Vigorously developing and utilizing the legume-microbe symbiotic system can produce significant ecological and environmental benefits, the primary manifestation of which is to reduce the application of fertilizers and achieve a dual reduction in agricultural non-point source pollution and greenhouse gas emissions. As mentioned above, legumes can obtain a large part of their own nitrogen needs through symbiotic nitrogen fixation, thereby reducing nitrogen fertilizer input. Large-scale planting of legumes is regarded as a "biological nitrogen fertilizer" strategy that can reduce dependence on fertilizers at the regional and national scales. According to an analysis by the Acta Ecologica Sinica, under the scenario of optimizing the planting structure of major grain crops in China, an increase in the planting proportion of legumes will significantly reduce agricultural N2O emissions, making an outstanding contribution to greenhouse gas emission reduction. The study by Mahama et al. (2020) specifically quantified this effect: compared with the conventional full nitrogen application, the planting system that introduced legume cover crops and reduced nitrogen fertilizers accordingly reduced soil N2O emissions by 25% to 50%. The main mechanisms of leguminous crops in reducing greenhouse gases include: first, by replacing part of the chemical fertilizers, fossil energy consumption and indirect N2O emissions in the process of fertilizer production and use are reduced; second, the nitrogen release of symbiotic nitrogen fixation is more stable, avoiding the peak phenomenon of excessive inorganic nitrogen in the soil being converted into N2O. Therefore, promoting the symbiotic system of leguminous crops is conducive to controlling agricultural greenhouse gas emissions. More broadly, the use of leguminous-microorganism symbiosis can also help reduce the dependence on fertilizers for other elements in agriculture. For example, mycorrhizal fungal symbiosis can improve the absorption efficiency of leguminous plants for nutrients such as phosphorus and potassium, thereby reducing the application of phosphorus and potassium fertilizers. This is meaningful for reducing the consumption of phosphate resources and preventing eutrophication of water bodies. Similarly, the large amount of organic matter and nutrients provided by leguminous green manure can replace part of the input of organic fertilizers and trace element fertilizers. Yu et al. (2021) pointed out that through the rotation or intercropping of Gramineae and Leguminosae, the nutrient cycle of farmland can be optimized, and the application and loss of chemical fertilizers can be significantly reduced while ensuring yield. In my country's efforts to reduce the use of chemical fertilizers and pesticides, developing leguminous crops as green manure is one of the important measures. At present, the promotion of green manures such as astragalus and sweet clover in southern rice fields and northern orchards has achieved good results, supplementing hundreds of thousands of tons of nitrogen nutrients to farmland every year and reducing the corresponding amount of chemical fertilizer application. It can be seen that the legume-microorganism symbiotic system provides a practical way to reduce agricultural inputs and build an environmentally friendly agriculture.
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