title: Decline of arbuscular mycorrhizal fungi in northern hardwood forests exposed to chronic nitrogen additions.
abstract: Arbuscular mycorrhizal (AM) fungi are important below-ground carbon (C) sinks that can be sensitive to increased nitrogen (N) availability. The abundance of AM fungi (AMF) was estimated in maple (Acer spp.) fine roots following more than a decade of experimental additions of N designed to simulate chronic atmospheric N deposition. Abundance of AMF was measured by staining and ocular estimation, as well as by analyzing for the AMF indicator fatty acid 16:1omega5c in phospholipid (biomass indicator) and neutral lipid (lipid storage indicator) fractions. Arbuscular mycorrhizal fungal biomass, storage structures and lipid storage declined in response to N addition measured by both methods. This pattern was found when AM response was characterized as colonization intensity, on an areal basis and in proportion to maple above-ground biomass. The phospholipid fraction of the fatty acid 16:1omega5c was positively correlated with total AMF colonization and the neutral lipid fraction with vesicle colonization. Decreased AMF abundance with simulated N deposition suggests reduced C allocation to these fungi or a direct soil N-mediated decline. The fatty acid (phospholipid and neutral lipid fractions) 16:1omega5c was found to be a good indicator for AMF active biomass and stored energy, respectively.
authors.affiliation: Ecosystem Science Center, School of Forestry and Environmental Science, Michigan Technological University, Houghton, MI 49931, USA.
authors.forename: Linda T A
authors.initials: LTA
authors.lastname: Van Diepen
authors.affiliation: USDA Forest Service, Northern Research Station, Houghton, MI 49931, USA.
authors.forename: Erik A
authors.initials: EA
authors.lastname: Lilleskov
authors.affiliation: Ecosystem Science Center, School of Forestry and Environmental Science, Michigan Technological University, Houghton, MI 49931, USA.
authors.forename: Kurt S
authors.initials: KS
authors.lastname: Pregitzer
authors.affiliation: Environmental Research Division, Argonne National Laboratory, Argonne, IL 60439-4843, USA.
authors.forename: R Michael
authors.initials: RM
authors.lastname: Miller
mesh_terms: D031002:Acer / Q000382:microbiology*; D018533:Biomass; D002244:Carbon / Q000378:metabolism; D050356:Lipid Metabolism / Q000187:drug effects; D008824:Michigan; D038821:Mycorrhizae / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism; D009584:Nitrogen / Q000633:toxicity*; D018517:Plant Roots / Q000382:microbiology; D014197:Trees / Q000382:microbiology*