Nitrogen isotope variations in camphor (Cinnamomum Camphora) leaves of different ages in upper and lower canopies as an indicator of atmospheric nitrogen sources

Abstract

Nitrogen isotopic composition of new, middle-aged and old camphor leaves in upper and lower canopies has been determined in a living area, near a motorway and near an industrial area (Jiangan Chemical Fertilizer Plant). We found that at sites near roads, more positive δ15N values were observed in the camphor leaves, especially in old leaves of upper canopies, and ∆δ15N=δ15Nupper−δ15Nlower>0, while those near the industrial area had more negative δ15N values and ∆δ15N<0. These could be explained by two isotopically different atmospheric N sources: greater uptake from isotopically heavy pools of atmospheric NOx by old leaves in upper canopies at sites adjacent to roads, and greater uptake of 15N-depleted NHy in atmospheric deposition by leaves at sites near the industrial area. This study presents novel evidence that 15N natural abundance of camphor leaves can be used as a robust indicator of atmospheric N sources.