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This article in SSSAJ

  1. Vol. 49 No. 2, p. 444-447
     
    Received: Mar 1, 1984
    Accepted: Oct 10, 1984


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doi:10.2136/sssaj1985.03615995004900020034x

Natural Abundance of Nitrogen-15 as a Tool for Tracing Alder-Fixed Nitrogen1

  1. Dan Binkley,
  2. Phillip Sollins and
  3. William B. McGill2

Abstract

Abstract

Ratios of 15N to 14N often differ between pools within ecosystems, and measurement of these natural-abundance ratios might allow transfers among pools to be traced. We tested this approach for its ability to trace biologically-fixed N in conifer plantations. Ratios of 15N to 14N were measured in soil total-N, ammonium, and nitrate, and in foliage of Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] and red alder (Alnus rubra Bong.) at four sites. Two ecosystems were sampled at each site, one a pure conifer stand and the other a mixed alder-conifer stand. Isotope ratios differed significantly among stands, but no pattern was consistent across all locations. Soil NH+4 at all sites (and soil nitrate at one site) was significantly depleted in 15N relative to other N pools. Isotope discrimination clearly occurs during N transfers at these sites, but the 15N natural-abundance method does not provide a simple picture of N cycling at the ecosystem level.

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