Inertia in an ombrotrophic bog ecosystem in response to 9 years' realistic perturbation by wet deposition of nitrogen, separated by form

Sheppard, Lucy J.; Leith, Ian D.; Mizunuma, Toshie; Leeson, Sarah; Kivimaki, Sanna; Cape, J. Neil; van Dijk, Netty; Leaver, David; Sutton, Mark A.; Fowler, David; van den Berg, Leon J.L.; Crossley, Alan; Field, Chris; Smart, Simon. 2014 Inertia in an ombrotrophic bog ecosystem in response to 9 years' realistic perturbation by wet deposition of nitrogen, separated by form. Global Change Biology, 20 (2). 566-580.

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Wet deposition of nitrogen (N) occurs in oxidized (nitrate) and reduced (ammonium) forms. Whether one form drives vegetation change more than the other is widely debated, as field evidence has been lacking. We are manipulating N form in wet deposition to an ombrotrophic bog, Whim (Scottish Borders), and here report nine years of results. Ammonium and nitrate were provided in rainwater spray as NH4Cl or NaNO3 at 8, 24 or 56 kg N ha−1 yr−1, plus a rainwater only control, via an automated system coupled to site meteorology. Detrimental N effects were observed in sensitive nonvascular plant species, with higher cumulative N loads leading to more damage at lower annual doses. Cover responses to N addition, both in relation to form and dose, were species specific and mostly dependent on N dose. Some species were generally indifferent to N form and dose, while others were dose sensitive. Calluna vulgaris showed a preference for higher N doses as ammonium N and Hypnum jutlandicum for nitrate N. However, after 9 years, the magnitude of change from wet deposited N on overall species cover is small, indicating only a slow decline in key species. Nitrogen treatment effects on soil N availability were likewise small and rarely correlated with species cover. Ammonium caused most N accumulation and damage to sensitive species at lower N loads, but toxic effects also occurred with nitrate. However, because different species respond differently to N form, setting of ecosystem level critical loads by N form is challenging. We recommend implementing the lowest value of the critical load range where communities include sensitive nonvascular plants and where ammonium dominates wet deposition chemistry. In the context of parallel assessment at the same site, N treatments for wet deposition showed overall much smaller effects than corresponding inputs of dry deposition as ammonia.

Item Type: Publication - Article
Digital Object Identifier (DOI):
Programmes: CEH Topics & Objectives 2009 - 2012 > Biodiversity > BD Topic 1 - Observations, Patterns, and Predictions for Biodiversity > BD - 1.4 - Quantify and model interactions to determine impacts ...
CEH Topics & Objectives 2009 - 2012 > Biodiversity > BD Topic 2 - Ecological Processes in the Environment > BD - 2.4 - Estimate the impact of the main drivers and pressures on biodiversity ...
CEH Topics & Objectives 2009 - 2012 > Biogeochemistry > BGC Topic 1 - Monitoring and Interpretation of Biogeochemical and Climate Changes > BGC - 1.3 - Quantify & attribute changes in biogeochemiical cycles ...
CEH Topics & Objectives 2009 - 2012 > Biogeochemistry
UKCEH and CEH Sections/Science Areas: Dise
ISSN: 1354-1013
Additional Keywords: ammonium, cover, Calluna, chronology, critical loads, growth, nitrate, peatland, Sphagnum capillifolium
NORA Subject Terms: Ecology and Environment
Date made live: 15 Jan 2014 12:31 +0 (UTC)

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