Leaf and pod growth affect seed yield after shoot removal and different nitrogen rates of dual-purpose rapeseed (Brassica napus L.)

1. Nitrogen (N) application compensated for shoot removal-induced yield loss but reduced N use efficiency (NUE), while simultaneously enhancing pod growth and carbon metabolism in dual-purpose rapeseed. 2. A higher amino acid/soluble sugar ratio in pod walls promoted seed protein accumulation but decreased oil content. 3. The seed oil yield under SR with 270 kg N ha⁻ 1 was nearly equal to that under CK with 90 kg N ha⁻ 1 . As a multifunctional crop, rapeseed provides vegetables by picking shoots. Shoot removal reduced yield, while nitrogen (N) application results in efficiency gains. However, the effect of N rate on pod growth, N use efficiency (NUE) and seed yield after shoot removal is unclear. A 2-year field experiment was set with four N rates (0 [N0], 90 [N1], 180 [N2], and 270 [N3] kg ha −1 ) and two shoot treatments (no shoot removal [CK], shoot removal [SR]). Results showed the shoot removal decreased population biomass (PB) at maturity across all N levels. Conversely, N application increased the PB after shoot removal and elevated soluble sugar and protein in shoots. Shoot removal increased the seeds per pod (13.5-26.9%), reduced the pods per plant (33.1-45.8%) and population seed yield (19.5-38.4%). N application effectively increased the yield related index, and led to an increase in population seed yield by 187.2 - 465.0% in the CK group, and by 185.6 - 430.7% in the SR group. Moreover, the seed yield reached its maximum under the N3 in both groups. The leaf N content per area (N a ) and net photosynthetic rate ( P n ) were increased, but leaf photosynthetic N use efficiency (PNUE) were decreased at 20 days after shoot removal, which lead to a significant decrease in N use efficiency(NUE). N supply increased the plant organ N content and PB, but decreased the NUE at maturity stage. P n of the pod wall at 25 days after flowering was elevated due to its optimized chloroplasts ultrastructure and increased rubisco and sucrose synthase activities under shoot removal and more N. However, the greater amino acid/soluble sugar ratio (A/S) of the pod wall significantly increased the seed protein content and decreased the oil content. Though the oil yield was reduced by 63.8-71.0% under SR×N3 treatment compared with CK×N3, it was comparable to that of CK with 90 kg N ha −1 treatment. The results indicated that N applying improves the carbon metabolism of the pod wall and alleviates yield reduction after shoot removal but reduces NUE and seed oil content of rapeseed. The findings guide the balancing of rapeseed's vegetable and oil production, and optimize N fertilization for sustainable, efficient rapeseed farming.