油菜叶片功能氮动态变化对光合速率及光合氮利用效率的影响OA

Rapeseed(Brassica napus L.)is China's leading oilseed crop,and high yield depends heavily on nitrogen(N)fertilizer inputs;however,nitrogen use efficiency remains relatively low.Rapeseed biomass is primarily derived from photosynthesis.En-hancing the net photosynthetic rate(Pn)and photosynthetic nitrogen use efficiency(PNUE)may provide a feasible approach to simultaneously improve yield and nitrogen use efficiency,thereby reducing N fertilizer application,increasing rapeseed produc-tion,and supporting sustainable development of the rapeseed industry. Here,we conducted a hydroponic experiment with differ-ent N levels using two rapeseed germplasms that differed significantly in leaf area and Pn. During leaf development,we quantified dynamic changes in leaf N content,photosynthetic capacity,functional N fractions,and ribulose-1,5-bisphosphate carboxy-lase/oxygenase (Rubisco) characteristics to elucidate how N allocation regulates Pn and PNUE. Leaf N content declined with growth,but Pn did not decrease consistently,and Pn increased with higher N supply. Photosynthetic N (Npsn) and storage N (Nstore) were the dominant components of leaf N,accounting for 83.12％-97.61％. During leaf expansion,Npsn changed little whereas Nstore declined markedly,which helped maintain Pn at lower total leaf N and improved PNUE. When leaf N content fell below 1.77 g m-2,both Npsn and Nstore decreased linearly,leading to significant reductions in Pn and PNUE. During leaf senescence,the decline in Npsn was 6.24％-19.07％ greater than that of Nstore,resulting in pronounced decreases in both Pn and PNUE. Rubisco content was significantly and positively correlated with Npsn. The germplasm Yunyou 9,which had higher Pn,showed higher Npsn and Rubisco content than Fuyou 3,which had larger leaf area,with increases of 5.63％-40.37％ and 0.38％-38.02％,respectively. Both Npsn and Nstore increased with increasing N supply,and Pn increased with Npsn. Overall,during leaf development,Rubisco helped maintain Npsn while Nstore declined,supporting higher Pn and improved PNUE. Therefore,optimizing within-leaf N alloca-tion by precisely regulating Rubisco content may be an effective strategy to further enhance rapeseed photosynthetic capacity and nitrogen use efficiency.