Low-nitrogen-tolerant maize cultivar improves photosynthesis and yield by optimizing nitrogen allocation to increase electron transport under low-nitrogen and low-light stress

This study aimed to identify the physiological mechanisms enabling low-N-tolerant maize cultivar to maintain higher photosynthesis and yield under low-N, low-light, and combined stress. In a three-year field trial of low-N-tolerant and low-N-sensitive maize cultivars under two N fertilization (normal N: 240 kg N ha −1 ; low-N: 150 kg N ha −1 ) and two light conditions (normal light; low-light: 35% light reduction), the tolerant cultivar showed higher net photosynthetic rate than the sensitive one. Random Forest analysis and Structural Equation Modeling identified PSI donor-side limitation (elevated Y ND ) as the key photosynthetic constraint. The tolerant cultivar maintained higher D1 and PsaA protein levels and preferentially allocated photosynthetic N to electron transport. This strategy reduced Y ND and sustained photosystem stability, thus improving carboxylation efficiency and resulting in higher photosynthesis.