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Nitrogen Isotope Patterns in Alaskan Black Spruce Reflect Organic Nitrogen Sources and the Activity of Ectomycorrhizal Fungi

Author:
  • Jordan R. Mayor
  • Edward A. G. Schuur
  • Michelle C. Mack
  • Terresa N. Hollingsworth
  • Erland Bååth
Publishing year: 2012
Language: English
Pages: 819-831
Publication/Series: Ecosystems
Volume: 15
Issue: 5
Document type: Journal article
Publisher: Springer

Abstract english

Global patterns in soil, plant, and fungal stable isotopes of N (delta N-15) show promise as integrated metrics of N cycling, particularly the activity of ectomycorrhizal (ECM) fungi. At small spatial scales, however, it remains difficult to differentiate the underlying causes of plant delta N-15 variability and this limits the application of such measurements to better understand N cycling. We conducted a landscape-scale analysis of delta N-15 values from 31 putatively N-limited monospecific black spruce (Picea mariana) stands in central Alaska to assess the two main hypothesized sources of plant delta N-15 variation: differing sources and ECM fractionation. We found roughly 20% of the variability in black spruce foliar N and delta N-15 values to be correlated with the concentration and delta N-15 values of soil NH4 (+) and dissolved organic N (DON) pools, respectively. However, N-15-based mixing models from 24 of the stands suggested that fractionation by ECM fungi obscures the N-15 signature of soil N pools. Models, regressions, and N abundance data all suggested that increasing dependence on soil DON to meet black spruce growth demands predicates increasing reliance on ECM-derived N and that black spruce, on average, received 53% of its N from ECM fungi. Future research should partition the delta N-15 values within the soil DON pool to determine how choice of soil delta N-15 values influence modeled ECM activity. The C balance of boreal forests is tightly linked to N cycling and delta N-15 values may be useful metrics of changes to these connections.

Keywords

  • Biological Sciences
  • 15N
  • black spruce
  • denitrifier method
  • dissolved organic nitrogen
  • ectomycorrhiza
  • isotope fractionation
  • mixing models

Other

Published
  • BECC
  • Microbial Ecology
  • ISSN: 1432-9840
Erland Bååth
E-mail: erland [dot] baath [at] biol [dot] lu [dot] se

Professor emeritus

MEMEG

+46 46 222 42 64

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Sölvegatan 37, Lund

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