Oecologia

, Volume 155, Issue 4, pp 771–783

Site-dependent N uptake from N-form mixtures by arctic plants, soil microbes and ectomycorrhizal fungi

  • Karina Engelbrecht Clemmensen
  • Pernille Lærkedal Sorensen
  • Anders Michelsen
  • Sven Jonasson
  • Lena Ström
Ecosystem Ecology - Original Paper

DOI: 10.1007/s00442-008-0962-9

Cite this article as:
Clemmensen, K.E., Sorensen, P.L., Michelsen, A. et al. Oecologia (2008) 155: 771. doi:10.1007/s00442-008-0962-9

Abstract

Soil microbes constitute an important control on nitrogen (N) turnover and retention in arctic ecosystems where N availability is the main constraint on primary production. Ectomycorrhizal (ECM) symbioses may facilitate plant competition for the specific N pools available in various arctic ecosystems. We report here our study on the N uptake patterns of coexisting plants and microbes at two tundra sites with contrasting dominance of the circumpolar ECM shrub Betula nana. We added equimolar mixtures of glycine-N, NH4+–N and NO3–N, with one N form labelled with 15N at a time, and in the case of glycine, also labelled with 13C, either directly to the soil or to ECM fungal ingrowth bags. After 2 days, the vegetation contained 5.6, 7.7 and 9.1% (heath tundra) and 7.1, 14.3 and 12.5% (shrub tundra) of the glycine-, NH4+- and NO315N, respectively, recovered in the plant–soil system, and the major part of 15N in the soil was immobilized by microbes (chloroform fumigation-extraction). In the subsequent 24 days, microbial N turnover transferred about half of the immobilized 15N to the non-extractable soil organic N pool, demonstrating that soil microbes played a major role in N turnover and retention in both tundra types. The ECM mycelial communities at the two tundras differed in N-form preferences, with a higher contribution of glycine to total N uptake at the heath tundra; however, the ECM mycelial communities at both sites strongly discriminated against NO3. Betula nana did not directly reflect ECM mycelial N uptake, and we conclude that N uptake by ECM plants is modulated by the N uptake patterns of both fungal and plant components of the symbiosis and by competitive interactions in the soil. Our field study furthermore showed that intact free amino acids are potentially important N sources for arctic ECM fungi and plants as well as for soil microorganisms.

Keywords

Betula nana (dwarf birch)13CMicrobial biomassMycelial ingrowth bags15N

Supplementary material

442_2008_962_MOESM1_ESM.doc (69 kb)
(DOC 69 kb)

Copyright information

© Springer-Verlag 2008

Authors and Affiliations

  • Karina Engelbrecht Clemmensen
    • 1
  • Pernille Lærkedal Sorensen
    • 1
  • Anders Michelsen
    • 1
  • Sven Jonasson
    • 1
  • Lena Ström
    • 2
  1. 1.Department of Terrestrial Ecology, Institute of BiologyUniversity of CopenhagenCopenhagen KDenmark
  2. 2.GeoBiosphere Science Centre, Physical Geography and Ecosystems AnalysisLund UniversityLundSweden