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Nitrogen Saturation Studies

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The chronic deposition of nitrogen from the atmosphere is a recent stress to New England forests resulting from the combustion of fossil fuels. Nitrogen is a limiting nutrient to most terrestrial ecosystems, but may be a pollutant in aquatic ecosystems and drinking water. Therefore there are many fundamental and applied questions regarding the impact of long-term additions of nitrogen to our landscape. We have investigated the long-term response of nitrogen-limited forests to this novel disturbance since 1990. Two stands (red pine and mixed hardwood) have been given fertilizer N applications that are one and three times the current atmospheric N deposition in central Europe.

Measured field processes include:

  • net N mineralization
  • net nitrification
  • N leaching
  • litter fall
  • aboveground NPP
  • fine-root turnover
  • foliar chemistry
  • soil fluxes of CH4, N2O, and CO2

In 1991 and 1992 we added 15N-labeled ammonium and nitrate separately to half of each control and low N plot to follow the movements of added N into soil and vegetation.

This project is supported by the Harvard Forest Long-Term Ecological Research Program.