Ecosystems

, Volume 1, Issue 4, pp 352-360

First online:

Predicting the Effects of Atmospheric Nitrogen Deposition in Conifer Stands: Evidence from the NITREX Ecosystem-Scale Experiments

  • B. A.  EmmettAffiliated withInstitute of Terrestrial Ecology, Bangor Research Unit, Orton Building, Deiniol Road, Bangor, Gwynedd LL57 2UP, United Kingdom
  • , D.  BoxmanAffiliated withDepartment of Ecology, University of Nijmegen, PO Box 9010, NL-6500 GL Nijmegen, The Netherlands
  • , M.  BredemeierAffiliated withForest Ecosystem Research Center, University of Göttingen, Büsgenweg 1, D-37077 Göttingen, Germany
  • , P.  GundersenAffiliated withDanish Forest and Landscape Research Institute, Kongevej 11, DK-2970 Hørsholm, Denmark
  • , O. J.  KjønaasAffiliated withNorwegian Forest Research Institute, Høgskoleveien 12, N-1432 Ås, Norway
  • , F.  MoldanAffiliated withSwedish Environmental Research Institute, Box 47086, S-40285 Göteborg, Sweden
  • , P.  SchleppiAffiliated withDepartment of Forest Ecology, Swiss Federal Institute for Forest, Snow, and Landscape Research, CH-8903 Birmensdorf, Switzerland
  • , A.  TietemaAffiliated withLandscape and Environmental Change Research Group, University of Amsterdam, Nieuwe Prinsengricht 130, NL-1018 VZ Amsterdam, The Netherlands
  • , R. F.  WrightAffiliated withNorwegian Institute for Water Research, Box 173 Kjelsås, N-0411 Oslo, Norway

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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.

Key words: NITREX; conifer; forest; nitrogen deposition; nitrate leaching; carbon–nitrogen ratio; critical loads.