title: Nitrogen deposition does not enhance Sphagnum decomposition.
abstract: Long-term additions of nitrogen (N) to peatlands have altered bryophyte growth, species dominance, N content in peat and peat water, and often resulted in enhanced Sphagnum decomposition rate. However, these results have mainly been derived from experiments in which N was applied as ammonium nitrate (NH4NO3), neglecting the fact that in polluted areas, wet deposition may be dominated either by NO3(-) or NH4(+). We studied effects of elevated wet deposition of NO3(-) vs. NH4(+) alone (8 or 56kgNha(-1)yr(-1) over and above the background of 8kgNha(-1)yr(-1) for 5 to 11years) or combined with phosphorus (P) and potassium (K) on Sphagnum quality for decomposers, mass loss, and associated changes in hummock pore water in an ombrotrophic bog (Whim). Adding N, especially as NH4(+), increased N concentration in Sphagnum, but did not enhance mass loss from Sphagnum. Mass loss seemed to depend mainly on moss species and climatic factors. Only high applications of N affected hummock pore water chemistry, which varied considerably over time. Overall, C and N cycling in this N treated bog appeared to be decoupled. We conclude that moss species, seasonal and annual variation in climatic factors, direct negative effects of N (NH4(+) toxicity) on Sphagnum production, and indirect effects (increase in pH and changes in plant species dominance under elevated NO3(-) alone and with PK) drive Sphagnum decomposition and hummock C and N dynamics at Whim.
authors.affiliation: Department of Environmental Sciences, University of Helsinki, P.O. Box 65 (Viikinkaari 2a), 00014 Helsinki, Finland. Electronic address: sirkku.manninen@helsinki.fi.
authors.forename: S
authors.initials: S
authors.lastname: Manninen
authors.affiliation: Centre for Ecology and Hydrology Edinburgh, Bush Estate, Penicuik EH26 0QB, Scotland, UK.
authors.forename: S
authors.initials: S
authors.lastname: Kivimäki
authors.affiliation: Centre for Ecology and Hydrology Edinburgh, Bush Estate, Penicuik EH26 0QB, Scotland, UK.
authors.forename: I D
authors.initials: ID
authors.lastname: Leith
authors.affiliation: Centre for Ecology and Hydrology Edinburgh, Bush Estate, Penicuik EH26 0QB, Scotland, UK.
authors.forename: S R
authors.initials: SR
authors.lastname: Leeson
authors.affiliation: Centre for Ecology and Hydrology Edinburgh, Bush Estate, Penicuik EH26 0QB, Scotland, UK.
authors.forename: L J
authors.initials: LJ
authors.lastname: Sheppard
mesh_terms: D064751:Ammonium Compounds / Q000378:metabolism*; D004785:Environmental Pollutants / Q000378:metabolism*; D009566:Nitrates / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism*; D012606:Scotland; D044003:Sphagnopsida / Q000187:drug effects / Q000502:physiology*; D053833:Wetlands
chemical_list: D064751:Ammonium Compounds; D004785:Environmental Pollutants; D009566:Nitrates; D009584:Nitrogen
keywords: Ammonium; Decomposition; Hummock pore water; Nitrate; Peatlands; Sphagnum