Legume Genomics and Genetics 2025, Vol.16, No.3, 108-127 http://cropscipublisher.com/index.php/lgg 115 uptake can be maintained at a high level, comparable to the treatment of small amounts of nitrogen application, while inorganic nitrogen residues and N2O emissions in the soil are lower. This potential of "replacing fertilizer with solids" is exactly what sustainable agriculture needs. With the development of efficient rhizobia strains and the application of inoculation technology, the nitrogen fixation effect of leguminous crops has been further enhanced in many systems. For example, under the condition of reducing nitrogen fertilizer by 20% to 40%, leguminous crops such as peanuts can still maintain stable yields or even slightly increase. The field test results of Ding et al. (2024) showed that under the treatment of conventional fertilization with 40% nitrogen reduction and rhizobia inoculation, the peanut yield reached the highest, which was 5.3% higher than the control without fertilizer reduction and inoculation, indicating that part of the nitrogen was supplemented by nitrogen-fixing bacteria and the utilization efficiency was higher. It can be seen that microbial nitrogen fixation has a significant supporting effect on the nitrogen nutrition of leguminous crops and improves the nitrogen utilization efficiency of the crop system. Mycorrhizal fungal symbiosis can also improve the absorption and utilization of soil nitrogen by leguminous plants. AM bacteria expand the absorption range of ammonium nitrogen and nitrate nitrogen by the root system, and can activate the expression of nitrate transporters and ammonium transporters in plants, thereby improving the utilization rate of residual nitrogen in the soil by leguminous plants to a certain extent. Studies have found that legumes inoculated with AM bacteria in nitrogen-deficient soils absorb more total nitrogen than those that are not inoculated. Mycorrhizal symbiosis can also change the rhizosphere microbial community, promote the reproduction of organic nitrogen mineralizing bacteria, associative nitrogen-fixing bacteria, etc., and provide plants with more available nitrogen sources. Therefore, the dual symbiosis of rhizobia and mycorrhizal fungi can complement each other and play a synergistic role in meeting the nitrogen needs of legumes. 4.2 Improved adaptation to drought and salinity Leguminous crops often have limited growth under abiotic stress conditions such as drought and salinity, and symbiosis with beneficial microorganisms can significantly enhance their stress resistance. In this regard, mycorrhizal fungi and rhizosphere growth-promoting bacteria (PGPR) have played an important role. Under drought stress, arbuscular mycorrhizal fungi can improve the drought resistance of legumes in various ways. AM fungal symbiosis can promote the improvement of root morphology and function of host plants, such as increasing root length and root hair density to absorb water more effectively; mycorrhizal hyphae can bring additional water to plants from deep soil or compact pores to maintain a high moisture condition in the plant body. AM fungal infection can induce the host to improve water use efficiency, reduce stomatal aperture and thus reduce transpiration water loss. More importantly, mycorrhizal symbiosis can trigger a series of physiological and biochemical changes in plants, making them better tolerant to drought: including upregulating antioxidant enzyme activity (such as superoxide dismutase SOD, peroxidase POD, etc.), accumulating osmotic regulating substances (such as proline, soluble sugars), and regulating plant hormone balance (such as increasing abscisic acid to close stomata). Hashem et al. (2019) studied chickpea and showed that plants inoculated with AM fungi combined with biochar showed higher leaf moisture, chlorophyll content and antioxidant capacity under drought, and thus the yield was significantly higher than that of the uninoculated control. Al-Arjani et al. (2020) reported that AM fungal symbiosis promotes antioxidant defense and gene expression adjustment of the desert plant Ephedra under drought stress, thereby maintaining its growth. On forage grasses such as alfalfa, it was similarly observed that inoculation with mycorrhizae can reduce the inhibition of nodule development and nitrogen fixation by drought and improve nitrogen fixation efficiency under drought conditions. These studies consistently show that mycorrhizal fungi can significantly improve the stability of legume crops under dry farming environments by improving the physiological adaptability of the host, enabling legumes to maintain good growth and nutrient acquisition under water stress conditions. For saline-alkali stress, beneficial microorganisms can also play a buffering role. High salt conditions can interfere with the symbiotic process of legumes, such as inhibiting nodule formation and reducing nitrogen fixation activity. However, salt-tolerant rhizosphere growth-promoting bacteria and some salt-tolerant rhizobia strains can help
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