Seasonal internal nitrogen (N) cycling is an important strategy for trees to uncouple growth from N acquisition. While N uptake, allocation and storage has been intensively studied in association with leaf phenology and vegetative growth, influence of reproduction on these key processes is still poorly understood. Therefore, we applied pulse ¹⁵N labelling to three fruiting and three non-fruiting trees in a 92-year-old Fagus crenata forest on 18 July and traced ¹⁵N content per organ dry mass (¹⁵N_excess) in all new shoot organs from the upper crowns periodically until leaf fall. The amount of ¹⁵N_excess recovered in the whole new shoots in fruiting trees did not differ from non-fruiting individuals, although up to 70% of ¹⁵N_excess was recovered in fruits of fruiting trees but 87% in leaves of non-fruiting individuals. In addition, dramatic increase in ¹⁵N_excess amount in nuts was accompanied by about twofold increase in nut N content. These results indicate that new N uptake from the soil contributed greatly to seed ripening, which in turn resulted in less allocation to leaves in fruiting trees. In non-fruiting individuals, on the other hand, ¹⁵N_excess allocated to leaves was not accompanied by concomitant increase in leaf N content because biomass growth had ceased when ¹⁵N was applied. These results suggest that N uptake in the late growing season contributed to internal N storage in non-fruiting trees. These reproduction-related variations in seasonal N cycle have implications for N dynamics in the plant–soil system during environmental change.

中文翻译：

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繁殖影响青海藜种子成熟期间施加的15 N脉冲的新器官之间的分配

季节性内部氮（N）循环是树木从氮获取中解脱生长的重要策略。虽然已经结合叶片物候和营养生长对氮的吸收，分配和储存进行了深入研究，但对这些关键过程的繁殖影响仍然知之甚少。因此，我们在7月18日对拥有92年历史的Fagus crenata森林中的三棵果树和三棵非果树应用了脉冲¹⁵ N标记，并在所有新芽器官中追踪了每器官干重¹⁵ N含量（_过量¹⁵ N ）。上部树冠定期直到叶子落下。¹⁵ N的量_多余的回收在果树并没有从非出菇个人不同的全新的拍摄，虽然高达70％，^15个ñ_过剩在果树的果实，但在非出菇个人的叶子87％被回收。此外，坚果中¹⁵ N_过量的急剧增加伴随着坚果N含量的增加约两倍。这些结果表明，从土壤中吸收的新氮对种子的成熟有很大的贡献，这反过来导致对果树叶片分配的减少。另一方面，在没有结果的个体中，_过量¹⁵ N分配给叶片的叶片氮含量并未随之增加，因为当施用¹⁵ N时，生物量的生长已经停止。这些结果表明，生长后期的氮吸收促进了非果树内部的氮存储。这些与季节性氮循环相关的繁殖变化对环境变化期间植物-土壤系统中的氮动态具有影响。