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

Jordan R. Mayor, Edward A.G. Schuur, Michelle C. Mack, Terresa N. Hollingsworth, Erland Bååth

Research output: Contribution to journalArticlepeer-review

30 Scopus citations

Abstract

Global patterns in soil, plant, and fungal stable isotopes of N (δ15N) 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 δ15N variability and this limits the application of such measurements to better understand N cycling. We conducted a landscape-scale analysis of δ15N values from 31 putatively N-limited monospecific black spruce (Picea mariana) stands in central Alaska to assess the two main hypothesized sources of plant δ15N variation: differing sources and ECM fractionation. We found roughly 20% of the variability in black spruce foliar N and δ15N values to be correlated with the concentration and δ15N values of soil NH4+ and dissolved organic N (DON) pools, respectively. However, 15N-based mixing models from 24 of the stands suggested that fractionation by ECM fungi obscures the 15N 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 δ15N values within the soil DON pool to determine how choice of soil δ15N values influence modeled ECM activity. The C balance of boreal forests is tightly linked to N cycling and δ15N values may be useful metrics of changes to these connections.

Original languageEnglish (US)
Pages (from-to)819-831
Number of pages13
JournalEcosystems
Volume15
Issue number5
DOIs
StatePublished - Aug 2012
Externally publishedYes

Keywords

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

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Environmental Chemistry
  • Ecology

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