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Research article1997Peer reviewed

Identification of coniferous forests with incipient nitrogen saturation through analysis of arginine and nitrogen‐15 abundance of trees

Nordin, Annika; Näsholm, Torgny; Edfast, Ann-Britt; Högberg, Peter


Stands of Norway spruce [Picea abies (L.) Karst.] differing in throughfall N deposition and NO3 leaching were investigated to determine if arginine concentrations and δ15N abundances of needles could be used to predict NO3 leaching from stands. Twenty‐three stands, all located in southern Sweden, were sampled and five of these had average NO3 concentrations > 0.1 mg NO3‐N L−1 in soil water at a 50‐cm depth. Arginine concentrations and δ15N abundances of needles were significantly higher for sites that exhibited NO3 leaching. The δ15N enrichment (ε), i.e., difference between foliage and soil organic matter in δ15N, showed less variation than δ15N of needles alone in regressions against NO3 leaching and was, thus, a better predictor of leaching. All sites that exhibited N leaching had arginine concentrations > 5 µmol g dw−1 and ε > −0.5 (‰) and thus, there was strong correlation between arginine and ε values. To test if arginine accumulation, as such, can affect the δ15N of needles, arginine and δ15N were determined for Scots pine (Pinus sylvestris L.) trees given different amounts of N fertilizer. Although fertilization caused a dramatic increase in arginine concentrations of needles, no immediate change in δ15N was observed. A hypothesis is proposed to explain the causal linkage between elevated arginine and δ15N of needles and leaching of N. Thus, arginine accumulation in trees corresponds to decreased uptake rates of NH4+ leaving NH4+ ions available for nitrification. During nitrification, discrimination against the heavier takes place resulting in a depleted NO3 pool and enriched NH4+ pool. Preferential uptake of NH4+ by conifer trees will then lead to elevated 15N abundance of needles. It is concluded that N leaching coniferous forests can be identified through analysis of arginine and δ15N of needles.

Published in

Journal of Environmental Quality
1997, Volume: 26, number: 1, pages: 302-309