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

Nasholm T, Hogberg P, Franklin O, Metcalfe D, Keel SG, Campbell C, Hurry V, Linder S, et al. (2013). Are ectomycorrhizal fungi alleviating or aggravating nitrogen limitation of tree growth in boreal forests? New Phytologist 198 (1): 214-221. DOI:10.1111/nph.12139.

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Abstract

-- 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 C-N 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.

Item Type: Article
Uncontrolled Keywords: Field experiment; 13C-15N pulse labelling; Modelling; Mycorrhiza; Nitrogen immobilization; Nitrogen limitation; Scots pine (Pinus sylvestris)
Research Programs: Ecosystems Services and Management (ESM)
Bibliographic Reference: New Phytologist; 198(1):214-221 (April 2013) (Published online 29 January 2013)
Depositing User: IIASA Import
Date Deposited: 15 Jan 2016 08:49
Last Modified: 26 Feb 2016 10:37
URI: http://pure.iiasa.ac.at/10524

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