title: Nitrogen isotope fractionation during N uptake via arbuscular mycorrhizal and ectomycorrhizal fungi into grey alder.
abstract: Arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) fungi affect plant nitrogen (N) dynamics. Plant N isotope patterns have been used to characterise the contribution of ECM fungi to plant N uptake. By quantifying and comparing the effects of an AM and an ECM fungus on growth, N uptake and isotopic composition of one host plant grown at different relative N supply levels, the aim of this study was to improve the mechanistic understanding of natural15N abundance patterns in mycorrhizal plants and their underlying causes. Grey alders were inoculated with one ECM fungus or one AM fungus or left non-mycorrhizal. Plants were grown under semi-hydroponic conditions and were supplied with three rates of relative N supply ranging from deficient to luxurious. Neither mycorrhizal fungus increased plant growth or N uptake. AM root colonisation had no effect on whole plant δ15N and decreased foliar δ15N only under N deficiency. The roots of these plants were15N-enriched. ECM root colonisation consistently decreased foliar and whole plant δ15N. It is concluded, that both mycorrhizal fungi contributed to plant N uptake into the shoot. Nitrogen isotope fractionation during N assimilation and transformations in fungal mycelia is suggested to have resulted in plants receiving15N-depleted N via the mycorrhizal uptake pathways. Negative mycorrhizal growth effects are explained by symbiotic resource trade on carbon and N and decreased direct plant N uptake.
authors.affiliation: Department of Microbiology and Ecosystem Science, Division of Terrestrial Ecosystem Research, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria. Electronic address: peter.schweiger@univie.ac.at.
authors.forename: Peter F
authors.initials: PF
authors.lastname: Schweiger
mesh_terms: D029661:Alnus / Q000254:growth & development / Q000378:metabolism* / Q000382:microbiology; D002244:Carbon / Q000378:metabolism; D038821:Mycorrhizae / Q000502:physiology*; D009584:Nitrogen / Q000378:metabolism*; D009587:Nitrogen Isotopes / Q000032:analysis; D018517:Plant Roots / Q000254:growth & development / Q000378:metabolism / Q000382:microbiology; D013559:Symbiosis
chemical_list: D009587:Nitrogen Isotopes; D002244:Carbon; D009584:Nitrogen
keywords: Alnus incana (grey alder); Arbuscular mycorrhiza; Ectomycorrhiza; Isotope fractionation; Nitrogen uptake; δ(15)N