title: Evidence for differential effects of reduced and oxidised nitrogen deposition on vegetation independent of nitrogen load.
abstract: Nitrogen (N) deposition impacts natural and semi-natural ecosystems globally. The responses of vegetation to N deposition may, however, differ strongly between habitats and may be mediated by the form of N. Although much attention has been focused on the impact of total N deposition, the effects of reduced and oxidised N, independent of the total N deposition, have received less attention. In this paper, we present new analyses of national monitoring data in the UK to provide an extensive evaluation of whether there are differences in the effects of reduced and oxidised N deposition across eight habitat types (acid, calcareous and mesotrophic grasslands, upland and lowland heaths, bogs and mires, base-rich mires, woodlands). We analysed data from 6860 plots in the British Countryside Survey 2007 for effects of total N deposition and N form on species richness, Ellenberg N values and grass:forb ratio. Our results provide clear evidence that N deposition affects species richness in all habitats except base-rich mires, after factoring out correlated explanatory variables (climate and sulphur deposition). In addition, the form of N in deposition appears important for the biodiversity of grasslands and woodlands but not mires and heaths. Ellenberg N increased more in relation to NHx deposition than NOy deposition in all but one habitat type. Relationships between species richness and N form were habitat-specific: acid and mesotrophic grasslands appear more sensitive to NHx deposition while calcareous grasslands and woodlands appeared more responsive to NOy deposition. These relationships are likely driven by the preferences of the component plant species for oxidised or reduced forms of N, rather than by soil acidification.
authors.affiliation: Unie van Bosgroepen, Ede 6710AD, The Netherlands; Radboud University Nijmegen, Nijmegen 6525AJ, The Netherlands. Electronic address: l.vandenberg@bosgroepen.nl.
authors.forename: Leon J L
authors.initials: LJ
authors.lastname: van den Berg
authors.affiliation: Centre for Ecology & Hydrology, Environment Centre Wales, Bangor LL57 2UW, UK.
authors.forename: Laurence
authors.initials: L
authors.lastname: Jones
authors.affiliation: Centre for Ecology & Hydrology, Bush Estate, Penicuik EH26 0QB, UK.
authors.forename: Lucy J
authors.initials: LJ
authors.lastname: Sheppard
authors.affiliation: Centre for Ecology & Hydrology, Lancaster Environment Centre, Bailrigg, Lancaster LA1 4AP, UK.
authors.forename: Simon M
authors.initials: SM
authors.lastname: Smart
authors.affiliation: B-Ware Research Centre, Nijmegen 6503GB, The Netherlands.
authors.forename: Roland
authors.initials: R
authors.lastname: Bobbink
authors.affiliation: Centre for Ecology & Hydrology, Bush Estate, Penicuik EH26 0QB, UK.
authors.forename: Nancy B
authors.initials: NB
authors.lastname: Dise
authors.affiliation: Stockholm Environment Institute, University of York, Heslington, York YO10 5DD, UK.
authors.forename: Mike R
authors.initials: MR
authors.lastname: Ashmore
mesh_terms: D000397:Air Pollution / Q000032:analysis / Q000706:statistics & numerical data; D044822:Biodiversity; D002980:Climate; D004784:Environmental Monitoring; D065948:Grassland; D009584:Nitrogen / Q000032:analysis*; D009589:Nitrogen Oxides; D006109:Poaceae / Q000187:drug effects; D012987:Soil; D012989:Soil Pollutants / Q000032:analysis*; D013455:Sulfur
chemical_list: D009589:Nitrogen Oxides; D012987:Soil; D012989:Soil Pollutants; D013455:Sulfur; D009584:Nitrogen
keywords: Acidification; Bogs; Countryside survey; Grassland; Heathland; N deposition; NH(x):NO(y) ratio