Nitrogen (N) is a crucial mineral element for plants, forming the main components of proteins, nucleic acids, phospholipids, chlorophyll, hormones, vitamins, and alkaloids. It plays a vital role in all stages of plant growth and development. Low-N stress can hinder plant growth and reduce yield and quality. Plants have evolved complex regulatory mechanisms for N uptake and assimilation to adapt to varying soil N conditions. After absorption, N regulates phytohormones, microRNAs (miRNAs), root development, and mycorrhizal symbiosis to cope with environmental stress. This review highlights the regulation mechanisms of N absorption and assimilation, emphasizing the roles of N in hormone signals, miRNAs, lateral root growth, drought resistance, anthocyanin synthesis, and mycorrhizal symbiosis. Understanding N uptake, utilization, and interactions with other biological processes can improve N use efficiency (NUE) and breed plants with "less-input-more-output" traits. Nitrogen uptake in plants involves nitrate and ammonium transporters, with different regulatory mechanisms for each. Nitrate transporters (NRTs) and ammonium transporters (AMTs) are key for N absorption. Nitrate is reduced to nitrite and then to ammonium, which is assimilated into amino acids via enzymes like glutamine synthetase (GS) and glutamate synthetase (GOGAT). N signaling involves transcriptional and post-transcriptional regulation, with factors like NRT1.1, NLP7, and ABF2/3 playing key roles. N also influences hormone signals, such as ethylene, auxin, abscisic acid (ABA), and cytokinins, which regulate root development, drought resistance, and anthocyanin synthesis. Mycorrhizal symbiosis enhances N uptake and utilization, while N deficiency can trigger stress responses. The review discusses the interaction between N and various physiological processes, highlighting the importance of N in plant adaptation to environmental stresses. Improving NUE is critical for sustainable agriculture, and further research is needed to understand N signaling and its regulation of plant responses to abiotic stresses.Nitrogen (N) is a crucial mineral element for plants, forming the main components of proteins, nucleic acids, phospholipids, chlorophyll, hormones, vitamins, and alkaloids. It plays a vital role in all stages of plant growth and development. Low-N stress can hinder plant growth and reduce yield and quality. Plants have evolved complex regulatory mechanisms for N uptake and assimilation to adapt to varying soil N conditions. After absorption, N regulates phytohormones, microRNAs (miRNAs), root development, and mycorrhizal symbiosis to cope with environmental stress. This review highlights the regulation mechanisms of N absorption and assimilation, emphasizing the roles of N in hormone signals, miRNAs, lateral root growth, drought resistance, anthocyanin synthesis, and mycorrhizal symbiosis. Understanding N uptake, utilization, and interactions with other biological processes can improve N use efficiency (NUE) and breed plants with "less-input-more-output" traits. Nitrogen uptake in plants involves nitrate and ammonium transporters, with different regulatory mechanisms for each. Nitrate transporters (NRTs) and ammonium transporters (AMTs) are key for N absorption. Nitrate is reduced to nitrite and then to ammonium, which is assimilated into amino acids via enzymes like glutamine synthetase (GS) and glutamate synthetase (GOGAT). N signaling involves transcriptional and post-transcriptional regulation, with factors like NRT1.1, NLP7, and ABF2/3 playing key roles. N also influences hormone signals, such as ethylene, auxin, abscisic acid (ABA), and cytokinins, which regulate root development, drought resistance, and anthocyanin synthesis. Mycorrhizal symbiosis enhances N uptake and utilization, while N deficiency can trigger stress responses. The review discusses the interaction between N and various physiological processes, highlighting the importance of N in plant adaptation to environmental stresses. Improving NUE is critical for sustainable agriculture, and further research is needed to understand N signaling and its regulation of plant responses to abiotic stresses.