Nitrogen Supply Alleviates Cold Stress by Increasing Photosynthesis and Nitrogen Assimilation in Maize Seedlings

Cold stress inhibits the early growth of maize, leading to reduced productivity. Nitrogen (N) is an essential nutrient that stimulates maize growth and productivity, but the relationship between N availability and cold tolerance is poorly characterized. Therefore, we studied the acclimation of maize under combined cold stress and N treatments. Exposure to cold stress caused a decline in growth and N assimilation, but increased abscisic acid (ABA) and carbohydrate accumulation. The application of different N concentrations from the priming stage to the recovery period resulted in the following observations: (i) high N supply alleviated cold stress-dependent growth inhibition, as shown by increased biomass, chlorophyll and Rubisco content and PSII efficiency; (ii) cold stress-induced ABA accumulation was repressed under high N, presumably due to enhanced stomatal conductance; (iii) the mitigating effects of high N on cold stress could be due to the increased activities of N assimilation enzymes and improved redox homeostasis. After cold stress, the ability of maize seedlings to recover increased under high N treatment, indicating the potential role of high N in the cold stress tolerance of maize seedlings.