Are ectomycorrhizal fungi alleviating or aggravating nitrogen limitation of tree growth in boreal forests?. Issue 1 (29th January 2013)

• Record Type: Journal Article
• Authors: Näsholm, Torgny; Högberg, Peter; Franklin, Oskar; Metcalfe, Daniel; Keel, Sonja G.; Campbell, Catherine; Hurry, Vaughan; Linder, Sune; Högberg, Mona N.
• Is Part Of: New phytologist. Volume 198:Issue 1(2013)
• Page Start: 214
• Page End: 221
• Publication Date: 2013-01-29
• Subjects: field experiment -- 13C‐15N pulse labelling -- modelling -- mycorrhiza -- nitrogen immobilization -- nitrogen limitation -- Scots pine (Pinus sylvestris); Botany -- Periodicals; 580
• DOI: 10.1111/nph.12139
• Languages: English
• ISSNs: 0028-646X

Abstract

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 CO2 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.