Predicting the Effects of Atmospheric Nitrogen Deposition in Conifer Stands: Evidence from the NITREX Ecosystem-Scale Experiments |
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Authors: | B A Emmett D Boxman M Bredemeier P Gundersen O J Kjønaas F Moldan P Schleppi A Tietema R F Wright |
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Institution: | Institute of Terrestrial Ecology, Bangor Research Unit, Orton Building, Deiniol Road, Bangor, Gwynedd LL57 2UP, United Kingdom, UK Department of Ecology, University of Nijmegen, PO Box 9010, NL-6500 GL Nijmegen, The Netherlands, NL Forest Ecosystem Research Center, University of G?ttingen, Büsgenweg 1, D-37077 G?ttingen, Germany, DE Danish Forest and Landscape Research Institute, Kongevej 11, DK-2970 H?rsholm, Denmark, Norwegian Forest Research Institute, H?gskoleveien 12, N-1432 ?s, Norway, NO Swedish Environmental Research Institute, Box 47086, S-40285 G?teborg, Sweden, SE Department of Forest Ecology, Swiss Federal Institute for Forest, Snow, and Landscape Research, CH-8903 Birmensdorf, Switzerland, CH Landscape and Environmental Change Research Group, University of Amsterdam, Nieuwe Prinsengricht 130, NL-1018 VZ Amsterdam, The Netherlands, NL Norwegian Institute for Water Research, Box 173 Kjels?s, N-0411 Oslo, Norway, NO
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Abstract: | The NITREX project, which encompasses seven ecosystem-scale experiments in coniferous forests at the plot or catchment level
in northwestern Europe, investigates the effect of atmospheric nitrogen (N) deposition in coniferous forests. The common factor
in all of the experiments is the experimentally controlled change in N input over a period of 4–5 years. Results indicate
that the status and dynamics of the forest floor are key components in determining the response of forests to altered N inputs.
An empirical relationship between the carbon–nitrogen (C/N) ratio of the forest floor and retention of incoming N provides
a simply measured tool through which the likely timing and consequences of changes in atmospheric N deposition for fresh waters
may be predicted. In the terrestrial ecosystem, a 50% increase in tree growth is observed following the experimental reduction
of N and sulfur inputs in a highly N-saturated site, illustrating the damaging effects of acidifying pollutants to tree health
in some locations. Few biotic responses to the experimental treatments were observed in other NITREX sites, but the rapid
response of water quality to changes in N deposition, and the link to acidification in sensitive areas, highlight the need
for N-emission controls, irrespective of the long-term effects on tree health. The observed changes in ecosystem function
in response to the experimental treatments have been considered within the framework of the current critical-load approach
and thus contribute to the formulation of environmental policy. |
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Keywords: | : NITREX conifer forest nitrogen deposition nitrate leaching carbon– nitrogen ratio critical loads |
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