Changes in N concentrations of peat and its associated vegetation over 12 months in response to increased deposition of ammonium sulfate or nitric acid

Large intact moorland oligotrophic peat microcosms, complete with associated Calluna vulgaris- or mixed grass-dominated vegetation, have been subjected to realistically simulated precipitation with or without enhanced N. The control ‘rainfall’ solute composition was appropriate for the site of microcosm collection. In addition, N treatments were applied by adding to this basic mixture two or six times the ambient N deposition for the site, as either (NH4)2SO4 or HNO3. For both Calluna-dominated and grass-dominated microcosms, the treatments over 12 months resulted in significant falls in peat C:N ratio, associated with substantial increases in exchangeable NH4+. The accumulation of NH4+-N in peat was greater under Calluna than under grass for all N treatments. Peat KCl-extractable NH4+ concentration increased significantly with increasing (NH4)2SO4 treatments under both types of vegetation. However, peat total N concentration was only increased significantly by both NH4+ treatments under Calluna and by the highest NH4+ treatment under grass. The results show that peat-based ecosystems respond rapidly to enhanced N deposition, with NH4+-N deposition resulting in greater soil N accumulation than the corresponding amount of NO3−-N deposition.