Role of Nitrogen Fertilization in Mitigating Drought-Induced Physiological Stress in Wheat Seedlings

Drought stress is one of the major abiotic factors limiting crop growth and yield, particularly in wheat. Water deficit leads to reduced chlorophyll content, impaired photosynthetic performance, and decreased biomass accumulation. Nitrogen fertilization may influence plant physiological responses to drought; however, its capacity to alleviate drought-induced growth reduction remains uncertain. A pot experiment was conducted to evaluate the impact of different nitrogen-based fertilizers on wheat seedlings grown under irrigation level 60% PPW (control) and 30% PPW (drought stress) conditions, with balanced levels of phosphorus and potassium maintained in all treatments. Water deficit led to substantial reductions in chlorophyll content compared to optimally irrigated plants. Similarly, the performance index (PI) decreased by 139.3% at Term 1 (1 day after foliar nitrogen application) and 27.2% at Term 2 (7 days after application). The net photosynthetic rate (Pn) declined markedly under drought conditions and was not significantly improved by nitrogen fertilization, indicating a partial and mainly short-term physiological response to nitrogen under water deficit. The application of nitrogen fertilizers, particularly urea and Nitron S, modulated the relative chlorophyll content and selected chlorophyll fluorescence (Fv/Fm, Fv/Fo, PI) and gas-exchange (E, gs, Ci) parameters under drought conditions, mainly shortly after application. However, aboveground dry biomass under drought conditions was not significantly affected by any nitrogen fertilizer. Urea induced the most consistent short-term physiological responses under both irrigation regimes, with effects more pronounced shortly after application, whereas Nitron S showed fertilizer-specific effects under drought stress. Overall, the results demonstrate that foliar nitrogen fertilization can modulate short-term physiological responses of wheat seedlings to drought but does not translate into sustained improvements in Pn or biomass accumulation. In the context of climate change and increasing water scarcity, identifying nitrogen fertilizers that support physiological functioning without overestimating growth benefits has critical implications for sustainable wheat production. Optimizing nitrogen fertilization may, therefore, contribute to improved nutrient management strategies under water-limited conditions.