Carbon-nitrogen relations of ectomycorrhizal mycelium across a natural nitrogen supply gradient in boreal forest

Abstract

The supply of carbon (C) from tree photosynthesis to ectomycorrhizal (ECM) fungi is known to decrease with increasing plant nitrogen (N) supply, but how this affects fungal nutrition and growth remains to be clarified. We placed mesh-bags with quartz sand, with or without an organic N (N-15-, C-13-labeled) source, in the soil along a natural N supply gradient in boreal forest, to measure growth and use of N and C by ECM extramatrical mycelia. Mycelial C : N declined with increasing N supply. Addition of N increased mycelial growth at the low-N end of the gradient. We found an inverse relationship between uptake of added N and C; the use of added N was high when ambient N was low, whereas use of added C was high when C from photosynthesis was low. We propose that growth of ECM fungi is N-limited when soil N is scarce and tree belowground C allocation to ECM fungi is high, but is C-limited when N supply is high and tree belowground C allocation is low. This suggests that ECM fungi have a major role in soil N retention in nutrient-poor, but less so in nutrient-rich boreal forests.

Keywords

Betsele N supply gradient; boreal forest; carbon limitation; ectomycorrhizal fungi; extramatrical ectomycorrhizal mycelium; natural abundance of C-13 and N-15; nitrogen limitation; stable isotope mixing model analysis

Published in

New Phytologist
2021, volume: 232, number: 4, pages: 1839-1848
Publisher: WILEY

SLU Authors

• Nordström Högberg, Mona

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    

• Högberg, Peter

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    

UKÄ Subject classification

Ecology

Publication identifier

• DOI: https://doi.org/10.1111/nph.17701

Permanent link to this page (URI)

https://res.slu.se/id/publ/113688