The Mechanisms of Improved Grain Yield and Nitrogen Use Efficiency in Salt‐Tolerant Rice Varieties Under Salt Stress

ABSTRACT Nitrogen (N) uptake and utilisation are crucial for improving rice yields, but the mechanisms of N absorption and transportation under salt stress conditions are still unclear. To address this gap, therefore, a field experiment was conducted from 2022 to 2023 to evaluate the characteristics of N metabolism, nitrogen use efficiency, and yield in rice under varying saline conditions. The experiment was comprised of three irrigation treatments i.e., freshwater irrigation (S0) and seawater and freshwater mixtures i.e., 5 dS m −1 (S1), and 11 dS m −1 (S2) to simulate salt stress in salt tolerant (ST), i.e., ‘Chaoyou 1000’ and ‘Longliangyou 506’, and in salt sensitive (SS), i.e., ‘Ruanhuayou1179’ and ‘Ruanhuayoujinsi’ rice varieties. Compared with S0, the 2‐year average decreases in total nitrogen accumulation, nitrogen grain production efficiency and nitrogen harvest index were 27.1%, 17.8% and 10.5% under S1 treatment and 46.8%, 53.7% and 41.2% under S2 treatment for ST, respectively, all of which were lower than those for SS. Additionally, the gene expression of N‐metabolising enzymes such as OsNR1 , OsGS1.1 and OsGOGAOT and N transporter genes such as OsNRT2.1 and OsNRT2.3 were higher in ST than SS during the heading stage under salt stress, potentially enhancing N transport and utilisation. Moreover, a significant and positive correlation was found between total N accumulation at maturity and yield under salt stress. Overall, the findings not only provide significant theoretical support for the breeding and improvement of salt‐tolerant rice varieties but also offer scientific guidance for optimising nitrogen management strategies in saline conditions.