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Greater carbon allocation to mycorrhizal fungi reduces tree nitrogen uptake in a boreal forest

Hasselquist, Niles J. ; Metcalfe, Daniel B. LU ; Inselsbacher, Erich ; Stangl, Zsofia ; Oren, Ram ; Näsholm, Torgny and Högberg, Peter (2016) In Ecology 97(4). p.1012-1022
Abstract

The central role that ectomycorrhizal (EM) symbioses play in the structure and function of boreal forests pivots around the common assumption that carbon (C) and nitrogen (N) are exchanged at rates favorable for plant growth. However, this may not always be the case. It has been hypothesized that the benefits mycorrhizal fungi convey to their host plants strongly depends upon the availability of C and N, both of which are rapidly changing as a result of intensified human land use and climate change. Using large-scale shading and N addition treatments, we assessed the independent and interactive effects of changes in C and N supply on the transfer of N in intact EM associations with ∼15 yr. old Scots pine trees. To assess the dynamics of... (More)

The central role that ectomycorrhizal (EM) symbioses play in the structure and function of boreal forests pivots around the common assumption that carbon (C) and nitrogen (N) are exchanged at rates favorable for plant growth. However, this may not always be the case. It has been hypothesized that the benefits mycorrhizal fungi convey to their host plants strongly depends upon the availability of C and N, both of which are rapidly changing as a result of intensified human land use and climate change. Using large-scale shading and N addition treatments, we assessed the independent and interactive effects of changes in C and N supply on the transfer of N in intact EM associations with ∼15 yr. old Scots pine trees. To assess the dynamics of N transfer in EM symbioses, we added trace amounts of highly enriched 15NO3 - label to the EM-dominated mor-layer and followed the fate of the 15N label in tree foliage, fungal chitin on EM root tips, and EM sporocarps. Despite no change in leaf biomass, shading resulted in reduced tree C uptake, ca. 40% lower fungal biomass on EM root tips, and greater 15N label in tree foliage compared to unshaded control plots, where more 15N label was found in fungal biomass on EM colonized root tips. Short-term addition of N shifted the incorporation of 15N label from EM fungi to tree foliage, despite no significant changes in below-ground tree C allocation to EM fungi. Contrary to the common assumption that C and N are exchanged at rates favorable for plant growth, our results show for the first time that under N-limited conditions greater C allocation to EM fungi in the field results in reduced, not increased, N transfer to host trees. Moreover, given the ubiquitous nature of mycorrhizal symbioses, our results stress the need to incorporate mycorrhizal dynamics into process-based ecosystem models to better predict forest C and N cycles in light of global climate change.

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author
; ; ; ; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
N pulse labeling, Carbon supply, Ectomycorrhizas, Field experiment, Mutualism, Nitrogen availability, Nitrogen limitation, Scots pine
in
Ecology
volume
97
issue
4
pages
11 pages
publisher
Ecological Society of America
external identifiers
  • scopus:84963984087
  • pmid:27220217
ISSN
0012-9658
DOI
10.1890/15-1222.1
language
English
LU publication?
yes
id
45f897ab-e5bb-4788-bd2a-21b7593b04ea
date added to LUP
2018-06-01 14:32:44
date last changed
2021-01-17 05:53:09
@article{45f897ab-e5bb-4788-bd2a-21b7593b04ea,
  abstract     = {<p>The central role that ectomycorrhizal (EM) symbioses play in the structure and function of boreal forests pivots around the common assumption that carbon (C) and nitrogen (N) are exchanged at rates favorable for plant growth. However, this may not always be the case. It has been hypothesized that the benefits mycorrhizal fungi convey to their host plants strongly depends upon the availability of C and N, both of which are rapidly changing as a result of intensified human land use and climate change. Using large-scale shading and N addition treatments, we assessed the independent and interactive effects of changes in C and N supply on the transfer of N in intact EM associations with ∼15 yr. old Scots pine trees. To assess the dynamics of N transfer in EM symbioses, we added trace amounts of highly enriched 15NO3 - label to the EM-dominated mor-layer and followed the fate of the 15N label in tree foliage, fungal chitin on EM root tips, and EM sporocarps. Despite no change in leaf biomass, shading resulted in reduced tree C uptake, ca. 40% lower fungal biomass on EM root tips, and greater 15N label in tree foliage compared to unshaded control plots, where more 15N label was found in fungal biomass on EM colonized root tips. Short-term addition of N shifted the incorporation of 15N label from EM fungi to tree foliage, despite no significant changes in below-ground tree C allocation to EM fungi. Contrary to the common assumption that C and N are exchanged at rates favorable for plant growth, our results show for the first time that under N-limited conditions greater C allocation to EM fungi in the field results in reduced, not increased, N transfer to host trees. Moreover, given the ubiquitous nature of mycorrhizal symbioses, our results stress the need to incorporate mycorrhizal dynamics into process-based ecosystem models to better predict forest C and N cycles in light of global climate change.</p>},
  author       = {Hasselquist, Niles J. and Metcalfe, Daniel B. and Inselsbacher, Erich and Stangl, Zsofia and Oren, Ram and Näsholm, Torgny and Högberg, Peter},
  issn         = {0012-9658},
  language     = {eng},
  month        = {04},
  number       = {4},
  pages        = {1012--1022},
  publisher    = {Ecological Society of America},
  series       = {Ecology},
  title        = {Greater carbon allocation to mycorrhizal fungi reduces tree nitrogen uptake in a boreal forest},
  url          = {http://dx.doi.org/10.1890/15-1222.1},
  doi          = {10.1890/15-1222.1},
  volume       = {97},
  year         = {2016},
}