Research on the Physiological Mechanisms of Nitrogen in Alleviating Plant Drought Tolerance.

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.