title: Recovery of ectomycorrhiza after 'nitrogen saturation' of a conifer forest.
abstract: Trees reduce their carbon (C) allocation to roots and mycorrhizal fungi in response to high nitrogen (N) additions, which should reduce the N retention capacity of forests. The time needed for recovery of mycorrhizas after termination of N loading remains unknown. Here, we report the long-term impact of N loading and the recovery of ectomycorrhiza after high N loading on a Pinus sylvestris forest. We analysed the N% and abundance of the stable isotope (15) N in tree needles and soil, soil microbial fatty acid biomarkers and fungal DNA. Needles in N-loaded plots became enriched in (15) N, reflecting decreased N retention by mycorrhizal fungi and isotopic discrimination against (15) N during loss of N. Meanwhile, needles in N-limited (control) plots became depleted in (15) N, reflecting high retention of (15) N by mycorrhizal fungi. N loading was terminated after 20yr. The δ(15) N and N% of the needles decreased 6yr after N loading had been terminated, and approached values in control plots after 15yr. This decrease, and the larger contributions compared with N-loaded plots of a fungal fatty acid biomarker and ectomycorrhizal sequences, suggest recovery of ectomycorrhiza. High N loading rapidly decreased the functional role of ectomycorrhiza in the forest N cycle, but significant recovery occurred within 6-15yr after termination of N loading.
authors.affiliation: Department of Forest Ecology and Management, Swedish University of Agricultural Sciences (SLU), SE-901 83 Umeå, Sweden. peter.hogberg@sek.slu.se
authors.forename: Peter
authors.initials: P
authors.lastname: Högberg
authors.forename: Christian
authors.initials: C
authors.lastname: Johannisson
authors.forename: Stephanie
authors.initials: S
authors.lastname: Yarwood
authors.forename: Ingeborg
authors.initials: I
authors.lastname: Callesen
authors.forename: Torgny
authors.initials: T
authors.lastname: Näsholm
authors.forename: David D
authors.initials: DD
authors.lastname: Myrold
authors.forename: Mona N
authors.initials: MN
authors.lastname: Högberg
mesh_terms: D002244:Carbon / Q000378:metabolism; D038821:Mycorrhizae / Q000187:drug effects* / Q000502:physiology*; D009584:Nitrogen / Q000378:metabolism / Q000494:pharmacology*; D009587:Nitrogen Isotopes; D041605:Pinus sylvestris / Q000187:drug effects* / Q000382:microbiology*; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism / Q000382:microbiology; D012987:Soil / Q000737:chemistry; D012988:Soil Microbiology; D013548:Sweden; D014197:Trees / Q000187:drug effects* / Q000382:microbiology*
chemical_list: D009587:Nitrogen Isotopes; D012987:Soil; D002244:Carbon; D009584:Nitrogen