Nitrogen fertilizers play a critical role in enhancing crop yields; however, excessive application has resulted in significant environmental challenges, including water contamination and increased greenhouse gas emissions. Therefore, improving nitrogen use efficiency is essential for sustainable agriculture. This review based on a systematic search of Web of Science and CNKI for peer-reviewed studies on maize nitrogen efficiency published between 1945 and 2024 (excluding conference abstracts), this review presents the first multiscale synthesis demonstrating how balanced nitrate–ammonium nutrition coordinates N–C metabolism and phytohormone signaling to boost nitrogen use efficiency and stimulate maize growth, with supporting evidence from other crops. By integrating results from hydroponic and field experiments, the review evaluates the influence of mixed nitrogen sources on nitrogen uptake, root morphology, photosynthesis, carbon metabolism, and hormone signaling. Findings indicate that optimal NO₃⁻:NH_4⁺ ratios improve nitrogen absorption through enhanced root development and activation of specific nitrogen transporters. Additionally, mixed nitrogen nutrition increases photosynthetic efficiency, promotes carbon assimilation, reduces energy expenditure, and stimulates auxin-mediated growth. This review shows that balanced nitrate–ammonium co-application synergistically enhances crop nitrogen-use efficiency and yield, provides a theoretical basis for high-efficiency nitrogen-fertilizer development, and helps alleviate environmental pressures, advance sustainable agriculture, and secure food and ecosystem safety. Its efficacy, however, is modulated by soil type, climate, and genotypic variation, necessitating systematic validation and application optimization in future research.

Cadmium (Cd), a pervasive and highly phytotoxic metal pollutant, poses severe threats to agricultural productivity, ecosystem stability, and human health through its entry into the food chain. Plants have evolved intricate defense mechanisms, among which the strategic manipulation of nutrient elements emerges as a critical physiological and biochemical strategy for mitigating Cd stress. This comprehensive review delves deeply into the multifaceted roles of essential macronutrient elements (nitrogen, phosphorus, potassium, calcium, magnesium, sulfur), essential micronutrient elements (zinc, iron, manganese, copper) and non-essential beneficial elements (silicon, selenium) in modulating plant responses to Cd toxicity. We meticulously dissect the physiological, biochemical, and molecular underpinnings of how these nutrients influence Cd bioavailability in the rhizosphere, Cd uptake and translocation pathways, sequestration and compartmentalization within plant tissues, and the activation of antioxidant defense systems. Nutrient elements exert their influence through diverse mechanisms: competing with Cd for root uptake transporters, promoting the synthesis of complexes that reduce Cd mobility, stabilizing cell walls and plasma membranes to restrict apoplastic flow and symplastic influx, modulating redox homeostasis by enhancing antioxidant enzyme activities and non-enzymatic antioxidant pools, regulating signal transduction pathways, and influencing gene expression profiles related to metal transport, chelation, and detoxification. The complex interactions between nutrients themselves further shape the plant’s capacity to withstand Cd stress. Recent advances elucidating nutrient-mediated epigenetic regulation, microRNA involvement, and the role of nutrient-sensing signaling hubs in Cd responses are critically evaluated. Furthermore, we synthesize the practical implications of nutrient management strategies, including optimized fertilization regimes, selection of nutrient-efficient genotypes, and utilization of nutrient-enriched amendments, for enhancing phytoremediation efficiency and developing low-Cd-accumulating crops, thereby contributing to safer food production and environmental restoration in Cd-contaminated soils. The intricate interplay between plant nutritional status and Cd stress resilience underscores the necessity for a holistic, nutrient-centric approach in managing Cd toxicity in agroecosystems.

Drought represents a paramount constraint on global agricultural productivity, imposing severe limitations on crop yield and quality across diverse agroecosystems. Nitrogen (N), functioning as an indispensable macronutrient fundamental to plant architecture, metabolism, and stress acclimatization, exerts a pivotal influence in modulating plant resilience to water deficit. Substantial evidence accumulated in recent years underscores that optimal N nutrition significantly enhances plant adaptive capacity under drought by improving intrinsic water use efficiency (WUEi), optimizing photosynthetic performance, augmenting antioxidant defense systems, promoting advantageous root architectural modifications, and stabilizing biological N fixation (BNF) symbioses. This comprehensive review synthesizes current knowledge on the intricate physiological and molecular mechanisms underpinning N-mediated drought mitigation. We meticulously examine regulatory roles of N in water relations and hydraulic conductivity, photosynthetic apparatus protection and carbon assimilation efficiency, N metabolic flux and assimilation homeostasis, reactive oxygen species (ROS) scavenging and osmotic adjustment, root system development and resource foraging strategies, BNF system robustness under water stress, and the complex signaling networks integrating N and drought responses. Furthermore, we critically evaluate existing research consensus, identify persisting controversies and knowledge gaps, and delineate future research trajectories and translational challenges. The overarching objective is to furnish a robust theoretical foundation for devising precision N management strategies and advancing the breeding of drought-resilient, nutrient-efficient crop cultivars suited to arid and semi-arid regions facing escalating climate variability.

N, as plants’ most essential nutrient, profoundly shapes root system architecture (RSA), with LRs being preferentially regulated. This review synthesizes the intricate molecular mechanisms underpinning N sensing, signaling, and its integration into developmental pathways governing LR initiation, primordium formation, emergence, and elongation. We delve deeply into the roles of specific transporters (NRT1.1, nitrate transporter 2.1 (NRT2.1)), transcription factors (Arabidopsis nitrate regulated 1 (ANR1), NLP7, TGACG motif-binding factor (TGA), squamosa promoter-binding protein-like 9 (SPL9)) and intricate hormone signaling networks (auxin, abscisic acid, cytokinins, ethylene) modulated by varying N availability (deficiency, sufficiency, excess) and chemical forms (NO₃⁻, NH₄⁺, organic N). Emphasis is placed on the systemic signaling pathways, including peptide-mediated long-distance communication (CEP—C-terminally encoded peptide receptor 1 (CEPR1)) and the critical role of the shoot in modulating root responses. Furthermore, we explore the emerging significance of carbon–nitrogen (C/N) balance, post-translational modifications (ubiquitination, phosphorylation), epigenetic regulation, and the complex interplay with other nutrients (phosphorus (P), sulfur (S)) and environmental factors in shaping N-dependent LR plasticity. Recent advances utilizing single-cell transcriptomics and advanced imaging reveal unprecedented cellular heterogeneity in LR responses to N. Understanding this sophisticated regulatory network is paramount for developing strategies to enhance nitrogen use efficiency (NUE) in crops. This synthesis underscores how N acts as a master regulator, dynamically rewiring developmental programs through molecular hubs that synchronize nutrient sensing with root morphogenesis—a key adaptive strategy for resource acquisition in heterogeneous soils.