title: Responses to ammonium and nitrate additions by boreal plants and their natural enemies.
abstract: Separate effects of ammonium (NH4+) and nitrate (NO3-) on boreal forest understorey vegetation were investigated in an experiment where 12.5 and 50.0 kg nitrogen (N) ha(-1) year(-1) was added to 2 m2 sized plots during 4 years. The dwarf-shrubs dominating the plant community, Vaccinium myrtillus and V. vitis-idaea, took up little of the added N independent of the chemical form, and their growth did not respond to the N treatments. The grass Deschampsia flexuosa increased from the N additions and most so in response to NO3-. Bryophytes took up predominately NH4+ and there was a negative correlation between moss N concentration and abundance. Plant pathogenic fungi increased from the N additions, but showed no differences in response to the two N forms. Because the relative contribution of NH4+ and NO3- to the total N deposition on a regional scale can vary substantially, the N load a habitat can sustain without substantial changes in the biota should be set considering specific vegetation responses to the predominant N form in deposition.
authors.affiliation: Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden. annika.nordin@genfys.slu.se
authors.forename: Annika
authors.initials: A
authors.lastname: Nordin
authors.forename: Joachim
authors.initials: J
authors.lastname: Strengbom
authors.forename: Lars
authors.initials: L
authors.lastname: Ericson
mesh_terms: D000393:Air Pollutants / Q000009:adverse effects*; D018533:Biomass; D044002:Bryophyta / Q000187:drug effects / Q000254:growth & development; D017753:Ecosystem; D004784:Environmental Monitoring / Q000379:methods* / Q000706:statistics & numerical data; D005658:Fungi / Q000187:drug effects / Q000254:growth & development; D009584:Nitrogen / Q000009:adverse effects*; D063245:Plant Development; D010944:Plants / Q000187:drug effects / Q000382:microbiology; D000644:Quaternary Ammonium Compounds / Q000009:adverse effects*; D013548:Sweden; D014197:Trees
chemical_list: D000393:Air Pollutants; D000644:Quaternary Ammonium Compounds; D009584:Nitrogen