Are ectomycorrhizal fungi alleviating or aggravating nitrogen limitation of tree growth in boreal forests?

Research output: Contribution to journalArticle


Symbioses between plant roots and mycorrhizal fungi are thought to enhance plant uptake of nutrients through a favourable exchange for photosynthates. Ectomycorrhizal fungi are considered to play this vital role for trees in nitrogen (N)-limited boreal forests. We followed symbiotic carbon (C)N exchange in a large-scale boreal pine forest experiment by tracing 13CO2 absorbed through tree photosynthesis and 15N injected into a soil layer in which ectomycorrhizal fungi dominate the microbial community. We detected little 15N in tree canopies, but high levels in soil microbes and in mycorrhizal root tips, illustrating effective soil N immobilization, especially in late summer, when tree belowground C allocation was high. Additions of N fertilizer to the soil before labelling shifted the incorporation of 15N from soil microbes and root tips to tree foliage. These results were tested in a model for CN exchange between trees and mycorrhizal fungi, suggesting that ectomycorrhizal fungi transfer small fractions of absorbed N to trees under N-limited conditions, but larger fractions if more N is available. We suggest that greater allocation of C from trees to ectomycorrhizal fungi increases N retention in soil mycelium, driving boreal forests towards more severe N limitation at low N supply.


  • Torgny Nasholm
  • Peter Hogberg
  • Oskar Franklin
  • Dan Metcalfe
  • Sonja G. Keel
  • Catherine Campbell
  • Vaughan Hurry
  • Sune Linder
  • Mona N. Hogberg
External organisations
  • Swedish University of Agricultural Sciences, Umeå
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Physical Geography


  • field experiment, 13C-15N pulse labelling, modelling, mycorrhiza, nitrogen immobilization, nitrogen limitation, Scots pine (Pinus, sylvestris)
Original languageEnglish
Pages (from-to)214-221
JournalNew Phytologist
Issue number1
Publication statusPublished - 2013
Publication categoryResearch
Externally publishedYes