Ecosystems

, Volume 15, Issue 5, pp 819–831

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
Article

DOI: 10.1007/s10021-012-9548-9

Cite this article as:
Mayor, J.R., Schuur, E.A.G., Mack, M.C. et al. Ecosystems (2012) 15: 819. doi:10.1007/s10021-012-9548-9

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.

Keywords

15Nblack sprucedenitrifier methoddissolved organic nitrogenectomycorrhizaisotope fractionationmixing models

Supplementary material

10021_2012_9548_MOESM1_ESM.doc (117 kb)
Supplementary material 1 DOC 117 kb)
10021_2012_9548_MOESM2_ESM.doc (240 kb)
Supplementary material 2 (DOC 240 kb)
10021_2012_9548_MOESM3_ESM.doc (292 kb)
Supplementary material 3 (DOC 292 kb)

Copyright information

© Springer Science+Business Media, LLC 2012

Authors and Affiliations

  • Jordan R. Mayor
    • 1
    • 2
  • Edward A. G. Schuur
    • 1
  • Michelle C. Mack
    • 1
  • Terresa N. Hollingsworth
    • 3
  • Erland Bååth
    • 4
  1. 1.Department of BiologyUniversity of FloridaGainesvilleUSA
  2. 2.Smithsonian Tropical Research InstituteBalboa, Ancon, PanamaRepublic of Panama
  3. 3.USDA Forest ServicePacific North West Research Station, Boreal Ecology Cooperative Research Unit, University of Alaska FairbanksFairbanksUSA
  4. 4.Department of BiologyMicrobial Ecology Group, Ecology Building, Lund UniversityLundSweden