Nitrogen-mediated coordination of photosynthesis and carbohydrate metabolism enhances sweet corn yield and quality

Sweet corn, as a distinct maize type, is highly sensitive to nitrogen (N) management, yet the physiological mechanisms linking N supply with photosynthetic carbon assimilation and carbohydrate metabolism remain insufficiently understood. To address this, a two-year field experiment (2022-2023) was conducted using two cultivars (MT6855 and TYH6) under four N rates (0, 90, 180, and 270 kg N ha^-1). Compared with no N, fresh ear yield increased by 2.5-, 4.6-, and 4.6-fold under 90, 180, and 270 kg N ha^-1, respectively, with 180 kg N ha^-1 identified as the optimal rate. At this rate, leaf SPAD, leaf area, and net photosynthetic rate increased significantly, accompanied by accelerated grain filling and enhanced accumulation of sucrose, fructose, and starch. Excessive N (270 kg N ha^-1) reduced the activities of key carbohydrate-metabolizing enzymes by 7.8-12.4 % relative to 180 kg N ha^-1, indicating impaired sink metabolism. Yield was strongly correlated with photosynthetic traits and enzyme activities, with vacuolar acid invertase identified as the major contributor. These findings demonstrate that optimal N fertilization enhances yield and quality through coordinated regulation of photosynthesis and carbohydrate metabolism, providing a mechanistic basis for developing efficient N management strategies in intensive sweet corn production.