LAUSR

Abstract Optimizing canopy nitrogen (N) distribution to match the light gradient is crucial for maximizing canopy carbon gain and improving N utilization efficiency (NUtE) in crops. Light interception and utilization depend not only on canopy N distribution but also on leaf N allocation in the thylakoid light-harvesting proteins (membrane proteins) and Rubisco (water-soluble proteins). However, the distribution of different forms of N in the canopy and its relationship with canopy light and N distribution have not yet been clarified. In this study, two Brassica napus L. cultivars, Zhongyouza R5 (R5) and Huayouza No. 9 (H9), were grown under four N levels in a two-year field experiment to provide some insight into the coordination between light and N distribution in the canopy. The results showed that R5 absorbed the equivalent N and produced higher shoot biomass than H9, thereby improving the NUtE. Compared with H9, R5 had a lower light extinction coefficient (KL) and a higher N extinction coefficient (KN), thereby its light and N coordination parameter (KN/KL) being greater in both growing seasons. The fraction of SDS (sodium dodecyl sulfate; a detergent) soluble proteins associated with membrane proteins in R5 was 40.4 % lower than H9. Through a d-separation method of path analysis, KL and KN could be simultaneously improved by reducing SDS-soluble proteins N or increasing the extinction coefficient of water-soluble proteins N. This suggests that optimizing leaf N allocation could improve canopy light and N distribution, thereby enhancing canopy carbon gain and NUtE.