Nitrogen Isotopes in Tree Rings—Challenges and Prospects

Abstract

Nutritive, but detrimental if at high levels, several nitrogen (N) forms involved in air and soil biogeochemical reactions constitute the N load trees assimilate. Although a large body of literature describes series of tree-ring N isotopes (δ15N) as archival systems for environmental changes, several questions relative to the isotopic integrity and reproducibility of trends still linger in the dendroisotopist community. This chapter reviews the fundamentals of forest N cycling and examines trees as N receptors in their very position, at the interface between the atmosphere and pedosphere. The related scrutiny of intrinsic and extrinsic mechanisms regulating isotopic changes also underlines flaws and forces of tree-ring δ15N series as environmental indicators.

Evaluating the use of marine subsidies by Arctic foxes without direct coastal access; insights from stable isotopes

“…However, the method of Long et al (2005) gives an estimated difference δ 13 C of − 0.39 ‰ between 2000 and 2010 due to the Suess effect (Keeling 1979), which is almost 3.8 times smaller than the smallest difference between any of our prey classes (1.48 ‰, between terrestrial resident and migratory prey). Similarly, while both anthropogenic and ecological factors similarly may cause temporal variation in δ 15 N values, they also tend to act over longer time scales than the 10-15 years that differed between the samples used for the mixing model (Savard and Siegwolf 2022). We also used shore bird winter values as our isotope source signature for migratory prey relying on marine resources.…”

Increasing Wood δ15N in Response to Pig Manure Application

“…Since N may be mobile in sapwood rings [13], we pooled several adjacent rings for analyzing changes in δ 15 N wood. Specifically, we analyzed the last five formed rings (period 2016-2020).…”

“…For each tree, the rings formed in this period were separated using scalpels, milled and homogenized using a ball mill (Retsch ZM1, Haan, Germany). Cores were not pre-treated to remove mobile N compounds (e.g., resin) since this pre-treatment does not modify significantly the final δ 15 N values [13]. All sampled rings were located in the sapwood.…”

“…Most tree species produce annual, conspicuous rings in regions with marked seasonality so investigating wood δ 15 N ( 15 N/ 14 N) in tree rings allows us to reconstruct changes in N cycling [12,13]. Stable N isotopes and N concentrations in wood are considered a proxy for N supply relative to demand and have revealed contrasting long-term trends in different biomes.…”