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Are ectomycorrhizal fungi alleviating or aggravating nitrogen limitation of tree growth in boreal forests?
Author(s) -
Näsholm Torgny,
Högberg Peter,
Franklin Oskar,
Metcalfe Daniel,
Keel Sonja G.,
Campbell Catherine,
Hurry Vaughan,
Linder Sune,
Högberg Mo.
Publication year - 2013
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/nph.12139
Subject(s) - taiga , biology , nutrient , symbiosis , ectomycorrhiza , botany , agronomy , boreal , mycorrhiza , mycelium , ecology , genetics , bacteria
Summary 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 13 CO 2 absorbed through tree photosynthesis and 15 N injected into a soil layer in which ectomycorrhizal fungi dominate the microbial community. We detected little 15 N 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 15 N 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.