Stage-dependent shifts in non-structural carbohydrates and C, N stoichiometry in Setaria viridis along a salinity gradient in the Xiaokai River irrigation area of the Yellow River Delta, China.

INTRODUCTION: Non-structural carbohydrates (NSC), carbon (C), nitrogen (N) and their ratio are fundamental to plant carbon metabolism and nutrient balance, yet the dynamic relationships among these indicators under salt stress remain poorly understood.

METHODS: We measured plant NSC content, and C, N stoichiometry in aboveground and belowground parts of Setaria viridis, along with soil pH, electrical conductivity, C and N content, across a salinity gradient spanning 91.5 km in the Xiaokai River irrigation area of the Yellow River Delta, China.

RESULTS AND DISCUSSION: We found that plant NSC content was consistently higher in aboveground parts than in belowground parts across growth stages, indicating an aboveground-prioritized carbon strategy. For plant NSC components, soluble sugars acted as the primary drivers of NSC accumulation and dominated carbon partitioning and utilization, whereas starch played a more prominent role in carbon storage during the late growth stage than in the early growth stage, indicating a stage-dependent shift from immediate energy supply to reserve maintenance during the transition from vegetative growth to reproduction and senescence. For plant C, N stoichiometry, C content remained relatively stable, whereas N content varied significantly along the salinity gradient, resulting in a substantially higher plant C:N ratio in the late growth stage than in the early growth stage. Soil C:N ratio was the dominant factor influencing plant NSC and C, N stoichiometry in the early growth stage, driven by plant nitrogen demand; soil pH and electrical conductivity became dominant factors in the late growth stage, driven by soil salinization and pH conditions that affect nitrogen uptake and ion balance, indicating that the regulation of plant carbon and nitrogen metabolism by soil properties was stage-dependent.

CONCLUSION: Our results revealed that S. viridis adapts to soil salinity through coordinated regulation of NSC components, carbon and nitrogen balance, and organ-specific allocation, with stage-specific responses to soil drivers. These findings provide a scientific basis for understanding plant adaptation to saline-alkaline environments, and offer practical guidance for species selection and ecological management for vegetation restoration in these regions.