Part III Deposition Processes

Water, Air, and Soil Pollution

, Volume 85, Issue 4, pp 2057-2063

First online:

Vegetation atmosphere exchange of ammonia: Canopy cycling and the impacts of elevated nitrogen inputs

  • M. A. SuttonAffiliated withInstitute of Terrestrial Ecology, Edinburgh Research Station
  • , D. FowlerAffiliated withInstitute of Terrestrial Ecology, Edinburgh Research Station
  • , J. K. BurkhardtAffiliated withInstitute of Terrestrial Ecology, Edinburgh Research Station
  • , C. MilfordAffiliated withInstitute of Terrestrial Ecology, Edinburgh Research Station

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Summary

Micrometeorological measurements of atmospheric ammonia (NH3) exchange with semi-natural and agricultural plant communities were made using sensitive new instrumentation capable of determining NH3 fluxes at <0.1 μg m−3. The results are used to test hypotheses concerning the canopy cycling of reduced nitrogen (NHx) and the existence of potential feedbacks between total N inputs (from agricultural sources or atmospheric deposition) and the net NH3 flux. The measurements over cropland, together with a model calculating the ‘canopy compensation point’ for NH3 indicate the importance of stomatal NH3 emission and recapture of NH3 by plant cuticles and water-layers. In contrast, measurements at an extremely clean upland moorland suggest that cuticular desorption of NH3 is also possible at low concentrations. Interpretation of dew measurements suggests that leaf uptake of NH44 + may occur as a result of pH gradients between the leaf surface and apoplast. The combined conceptual model of NHx exchange provides a useful basis for developing quantitative resistance models to predict NH3 fluxes.