• Nitrogen (N) assimilation is associated with ¹⁴N/¹⁵N fractionation such that plant tissues are generally ¹⁵N‐depleted compared to source nitrate. In addition to nitrate concentration, the δ¹⁵N value in plants is also influenced by isotopic heterogeneity amongst organs and metabolites. However, our current understanding of δ¹⁵N values in nitrate is limited by the relatively small number of compound‐specific data.
• We extensively measured δ¹⁵N in nitrate at different time points, in sunflower and oil palm grown at fixed nitrate concentration, with nitrate circulation being varied using potassium (K) conditions and waterlogging.
• There were strong interorgan δ¹⁵N differences for contrasting situations between the two species, and a high ¹⁵N‐enrichment in root nitrate. Modelling shows that this ¹⁵N‐enrichment can be explained by nitrate circulation and compartmentalisation whereby despite a numerically small flux value, the backflow of nitrate to roots via the phloem can lead to a c. 30‰ difference between leaves and roots. Accordingly, waterlogging and low K conditions, which down‐regulate sap circulation, cause a decrease in the leaf‐to‐root isotopic difference.
• Our study thus suggests that plant δ¹⁵N can be used as a natural tracer of N fluxes between organs and highlights the potential importance of δ¹⁵N of circulating phloem nitrate.

中文翻译：

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植物中的δ15N值由硝酸盐吸收和循环确定

• 氮（N）同化与¹⁴ N / ¹⁵ N分离有关，因此与源硝酸盐相比，植物组织通常消耗^15N。除了硝酸盐浓度，则δ ¹⁵在植物中N值也由同位素的异质性之间的器官和代谢物的影响。然而，我们的的δ目前了解¹⁵在硝酸N个值是由相对小数目的化合物的特定的数据的限制。
• 我们广泛δ测量¹⁵在不同时间点N的硝酸，在向日葵和油棕榈在固定硝酸盐浓度生长，用硝酸循环使用钾（K）的条件下和水涝而变化。
• 有强interorganδ ^15个为对比两种物种之间的情况Ñ差异，和高的¹⁵中的硝酸根的N-富集。模型表明，这¹⁵ N的富集可以用硝酸盐循环和分隔来解释，尽管尽管通量数值较小，但硝酸盐通过韧皮部回流到根部可能导致c。叶与根之间的差异为30‰。因此，内涝和低钾条件下调了树液的循环，从而降低了叶根同位素差异。
• 因此，我们的研究表明，植物δ ¹⁵ N可以被用作N的天然示踪剂机关和亮点之间的通量δ潜在重要性¹⁵ ň循环硝酸盐韧皮部。