Role of leaf nitrogen allocation under heterogeneous light in supporting photosynthetic compensation via optimizing carbon assimilation.

Photosynthetic compensation enables plants to adapt to heterogeneous light, but its mechanisms remain unclear. This study investigates two maize (Zea mays L.) cultivars, 'Rongyu 1210' (RY) and 'Zhongdan 808' (ZD), under horizontal heterogeneous light (HL). Results showed that nitrogen (N) and photosynthetic N (NP) concentrations increased in unshaded leaves (US-L) but decreased in shaded leaves (S-L) for both cultivars. However, significant differences were observed in N allocation among photosynthetic components between the two cultivars. These differences were particularly evident in N components involved in CO2 assimilation (NC) of US-L. In HL-treated RY, NC increased in US-L. As a result, the production and export of photosynthates, mainly sucrose, are enhanced to compensate for the reduction in S-L. In contrast, NC decreased in US-L of HL-treated ZD, which performs an impaired photosynthetic compensation. Our study suggests that coordinated regulation between systemic N redistribution and local N allocation, rather than a single trait adjustment, is critical for maintaining high photosynthetic compensation under HL. This provides a physiological basis for improving light use efficiency and yield potential under HL.