Bioscience Methods 2025, Vol.16, No.4, 204-217 http://bioscipublisher.com/index.php/bm 205 economy, it can reduce grain production costs and improve fertilizer utilization efficiency; for production, it can achieve "higher output with less input" by increasing the output per unit of nitrogen fertilizer, and ensure grain production capacity and farmers' income. This study will systematically explain the physiological mechanism and implementation path of rice nitrogen efficient utilization, analyze the absorption, transport and redistribution process of rice, and the relationship between nitrogen metabolism and plant growth and development; summarize the functions and regulation of genes related to rice nitrogen efficient utilization identified in recent years, including key transporters, assimilation enzymes and transcription factor networks; explore the green fertilization technology for controlling nitrogen supply and reducing environmental impact, and its application effect in field trials and large-scale demonstrations; compare the response differences of different types of rice varieties (such as indica-japonica hybrid rice and conventional japonica rice) to nitrogen fertilizer and their compatibility with fertilization strategies; through the case of Jiashan area, introduce the practical model and results of the synergistic effect of green fertilization technology and high-efficiency varieties. This study summarizes the core mechanism of rice nitrogen efficient utilization and the value of green fertilization in sustainable agriculture, and looks forward to future research directions and promotion and application, providing a theoretical basis and practical reference for rice fertilizer saving and efficiency improvement. 2 Physiological Mechanisms of Nitrogen Uptake and Transport in Rice 2.1 Root mechanisms for nitrogen uptake Rice roots are the main organs for nitrogen absorption, and their nitrogen absorption efficiency is affected by factors such as root morphology, physiological activity, and soil nitrogen supply. In rice soil, nitrogen mainly exists in the form of ammonium (NH4 +) and nitrate (NO3 -). Rice prefers to absorb ammonium nitrogen. High-affinity and low-affinity ammonium transporters (such as AMT) are distributed on the epidermal and cortical cell membranes of the roots, which can actively absorb NH4 + in the soil solution. At the same time, due to the release of oxygen by the aerenchyma of the rice roots, local nitrification occurs in the rhizosphere, and rice also has a strong absorption capacity for NO3 - (Wang et al., 2020). There are two major types of nitrate transporters in the root system, NRT1/NPF and NRT2. Among them, the NPF family is responsible for the low-affinity uptake of large amounts of NO3 -, and the NRT2 family is responsible for the high-affinity uptake of NO3 - (Lee, 2021). For example, OsNRT2.3b and OsNRT2.3a are located in the phloem and xylem, respectively, and mediate the upward transport of nitrogen from the roots to the stems and leaves. Another important pathway is the direct absorption of organic nitrogen by the roots, such as amino acids, which enter the root cells through specific carrier proteins. Rhizosphere microorganisms can increase the effective nitrogen supply in the soil through nitrogen fixation and ammonification. Inoculation of nitrogen-fixing bacteria can enhance the supply of NH4 + in the rhizosphere and increase the nitrogen uptake of rice (Wang et al., 2024). Nitrogen uptake by rice roots is the result of the combined action of multiple membrane transport proteins and rhizosphere biological processes, and its efficiency determines the nitrogen nutritional status and subsequent utilization efficiency of the plant. 2.2 Transport and redistribution of nitrogen within the plant The nitrogen absorbed by the rice roots needs to be effectively distributed in the body to maximize its use for growth and yield formation. The NH4 + absorbed by the roots is assimilated into glutamine in the roots through the glutamine synthetase-glutamate synthetase (GS-GOGAT) pathway, and then converted into other amino acids, which are transported upward to the stems and leaves through the xylem sap flow. Part of NO3 - can be reduced to nitrite by nitrate reductase (NR) in the roots and then further assimilated by the leaves; unreduced NO3 - enters the leaves with the transpiration flow and is assimilated into organic nitrogen in the leaves. The redistribution of nitrogen between various organs of the plant is crucial for the late filling of rice. After heading, a large amount of protein stored in the nutrient leaves and stem sheaths is decomposed to produce amino acids, which are transported to the grains through the phloem for protein synthesis. It is estimated that about 70%-80% of the nitrogen in rice grains comes from the retransportation of nutrient organs (Padhan et al., 2023). Efficient nitrogen reuse depends on the participation of amino acid transporters, such as OsNRT2.3b and OsNPF7.2 located in the phloem, which play an important role in nitrogen redistribution. Nitrogen redistribution efficiency (nitrogen
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