Fate of Precipitation-borne N in a Maine Spruce-Hemlock Forest: Results of First-year Ammonium Nitrate Canopy Fertilization
Abstract
Nitrogen oxides emitted as a result of fuel combustion and ammonia volatilization due to agriculture account for a large increase in N available to temperate forests in the northern hemisphere. Northern forests are thought to be limited in growth by the availability of N and increased inputs have coincided with increased carbon contents reported in northern forest inventories. The fate of anthropogenic N, residence time and the significance of an N-fertilization effect upon forest growth, however, remains unknown. We report throughfall findings from an ecosystem-level nitrogen addition made as wet precipitation to the canopy of a spruce-hemlock forest in central Maine. Ammonium nitrate and potassium nitrate were sprayed on 21 hectares of canopy by helicopter in six applications throughout the growing season; a final addition rate of 18 kg N per hectare per year. We measured N in canopy needles, senesced needles, throughfall (TF) and soils and soil water throughout this first-year application. TF-N in precipitation events following fertilization suggested retention to be highly variable but removing substantial N from the canopy addition. Moreover, while inorganic N in TF remained similar in ratio, 33% ammonium and 66% nitrate, as that added to the canopy; the single largest flux of N to the forest floor was in the form of DON. TF data from subsequent rain events were often indistinguishable from non-fertilized controls. The retention of N in the canopy and the preponderance of DON in TF should be considered when investigating effects of anthropogenic N on forest growth.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2001
- Bibcode:
- 2001AGUFM.B51B0202D
- Keywords:
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- 0315 Biosphere/atmosphere interactions;
- 0330 Geochemical cycles;
- 0345 Pollution: urban and regional (0305);
- 0400 BIOGEOSCIENCES