Δ15N values in plants are determined by both nitrate assimilation and circulation. Issue 6 (14th March 2020)

• Record Type: Journal Article
• Authors: Cui, Jing; Lamade, Emmanuelle; Fourel, François; Tcherkez, Guillaume
• Is Part Of: New phytologist. Volume 226:Issue 6(2020)
• Page Start: 1696
• Page End: 1707
• Publication Date: 2020-03-14
• Subjects: fractionation -- modelling -- nitrate -- nitrogen isotope -- oil palm -- potassium -- sunflower -- waterlogging; Botany -- Periodicals; 580
• DOI: 10.1111/nph.16480
• Languages: English
• ISSNs: 0028-646X

Abstract

Summary: Nitrogen (N) assimilation is associated with 14 N/ 15 N fractionation such that plant tissues are generally 15 N‐depleted compared to source nitrate. In addition to nitrate concentration, the δ 15 N value in plants is also influenced by isotopic heterogeneity amongst organs and metabolites. However, our current understanding of δ 15 N values in nitrate is limited by the relatively small number of compound‐specific data. We extensively measured δ 15 N 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 δ 15 N differences for contrasting situations between the two species, and a high 15 N‐enrichment in root nitrate. Modelling shows that this 15 N‐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 δ 15 N can be used as a natural tracer of N fluxes between organs and highlights the potential importance of δ 15 N of circulating phloem nitrate.