Forests losing large quantities of nitrogen have elevated 15N:14N ratios |
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Authors: | Peter Högberg |
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Institution: | (1) Department of Forest Site Research, Swedish University of Agricultural Sciences, S-901 83 Umeå, Sweden |
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Abstract: | Summary Urea (U) and ammonium nitrate (AN) had been applied to a Scots pine (Pinus sylvestris L.) forest in northern Sweden for 18 consecutive years at four doses resulting in total N applications ranging from 0 to 1980 kg ha–1. The 15N abundance ( 15N) of the grass Deschampsia flexuosa (L.) Trin. increased linearly (from –0.7 to 11.0) with application rate in the case of U. The response to AN was in the same direction but smaller. While others have shown that the initial response of nitrogen-limited systems to additions of N is a change of 15N abundance towards that of added N, this study shows that further and excessive additions leads to a retention of 15N. Monitoring 15N abundance over time in dose-response trials of this type thus opens new possibilities to estimate critical loads of N and the point of nitrogen saturation. |
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Keywords: | 15N Forests Nitrogen |
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