Mycorrhizal fungi supply nitrogen to host plants in Arctic tundra and boreal forests: ¹⁵N is the key signalThis article is one of a selection of papers in the Special Issue on Polar and Arctic Microbiology.

Abstract

Symbiotic fungi's role in providing nitrogen to host plants is well-studied in tundra at Toolik Lake, Alaska, but little-studied in the adjoining boreal forest ecosystem. Along a 570 km north-south transect from the Yukon River to the North Slope of Alaska, the .15 N content was strongly reduced in ectomycorrhizal and ericoid mycorrhizal plants including Betula, Salix, Picea mariana (P. Mill.) B.S.P., Picea glauca Moench (Voss), and ericaceous plants. Compared with the . 15 N content of soil, the foliage of nonmycorrhizal plants (Carex and Eriophorum) was unchanged, whereas content of the ectomycorrhizal fungi was very much higher (e.g., Boletaceae, Leccinum and Cortinarius). It is hypothesized that similar processes operate in tundra and boreal forest, both nitrogen-limited ecosystems: (i) mycorrhizal fungi break down soil polymers and take up amino acids or other nitrogen compounds; (ii) mycorrhizal fungi fractionate against .15 N during production of transfer compounds; (iii) host plants are accordingly depleted in .15 N; and (iv) mycorrhizal fungi are enriched in . 15 N. Increased N availability for plant roots or decreased light availability to understory plants may have decreased N allocation to mycorrhizal partners and increased d. 15 N by 3%-4% for southern populations of Vaccinium vitis-idaea L. and Salix. Fungal biomass, measured as ergosterol, correlated strongly with soil organic matter and attained amounts similar to those in temperate forest soils.Key words: mycorrhizal fungi, .15 N, nitrogen cycling, symbiosis, nitrogen isotopes.Résumé : Le rôle des champignons symbiotiques dans l'apport en azote des hôtes est bien étudié dans la toundra, au lac Toolik, en Alaska, mais peu étudié dans l'écosystème adjacent que constitue la forêt boréale. Le long des 570 km du transect nord-sud allant de la rivière Yukon au versant nord de l'Alaska, le d. 15 N était fortement réduit chez les plantes ectomycorhizes et mycorhizes éricoïdes, notamment Betula, Salix, Picea mariana (P. Mill.) B.S.P., Picea glauca Moench (Voss) et les éricacées. Le feuillage des plantes non mycorhizes (Carex et Eriophorum) demeure inchangé en fonction du contenu du sol en . 15 N, alors que le contenu des champignons ectomycorhizes est beaucoup plus élevé (e.g., Bolétacées, Leccinum et Cortinarius). On a supposé que des processus similaires opèrent dans la toundra et la forêt boréale, deux écosystèmes limités en azote : (i) les champignons mycorhizes scindent les polymères du sol et incorporent les acides aminés ou les autres composés azotés; (ii) les champignons mycorhizes favorisent le .15 N lors du transfert des composés; (iii) les plantes hôtes sont conséquemment appauvries en . 15 N; et (iv) les champignons mycorhizes sont enrichis en . 15 N. La disponibilité accrue de l'azote pour les racines des plantes ou la plus faible disponibilité de lumière pour les plantes en sous-étage peut avoir diminué la portion d'azote allouée aux partenaires des mycorhizes et augmenté le d. 15 N de 3%-4% chez les populations de Vaccinium vit...

European Bison as a Refugee Species? Evidence from Isotopic Data on Early Holocene Bison and Other Large Herbivores in Northern Europe

“…In boreal forest ecosystems, the δ 15 N values are higher in non- mycorrhizal plants such as graminoids, herbs, forbs, clubmosses, than in ectomycorrhizal and ericoid plants, such as trees and shrubs. Intermediate values of δ 15 N are found in mosses which, unlike most vascular plants, can rely on different sources of nitrogen, as well as in lichens [ 49 ], [ 50 ], [ 51 ], [ 52 ] (see also S1 Text ). Even after standardization to a common mean annual temperature, non-mycorrhizal plants had the highest average δ 15 N [ 53 ].…”

Soil bacterial community composition altered by increased nutrient availability in Arctic tundra soils

“…Changes in the types of roots and root biomass affect mycorrhizal fungi associations as well ( Hobbie, 2006 ; Hobbie and Hobbie, 2006 ; Hobbie et al, 2009 ). In Arctic tundra ecosystems, however, responses of root biomass to fertilization have varied from no change ( Mack et al, 2004 ; Gough et al, 2012 ) to significant increase ( Jonasson et al, 1999 ; Nadelhoffer et al, 2002 ) at a community level.…”

Summer temperature increase has distinct effects on the ectomycorrhizal fungal communities of moist tussock and dry tundra in Arctic Alaska

“…Arctic soils have limited availability of nutrients and arctic plants are highly dependent on mutualistic relationships with mycorrhizal fungi for survival (Gardes x0026; Dahlberg, 1996; Hobbie et al ., 2009; Bjorbækmo et al ., 2010). It has been estimated that 61–86% of the N in Arctic tundra plants is obtained through mycorrhizal fungi (Hobbie x0026; Hobbie, 2006).…”