CHANGES IN N CONCENTRATIONS OF PEAT AND ITS ASSOCIATED VEGETATION OVER 12 MONTHS IN RESPONSE TO INCREASED DEPOSITION OF AMMONIUM-SULFATE ORNITRIC-ACID

Large intact moorland oligotrophic peat microcosms, complete with asso ciated Calluna vulgaris- or mixed grass-dominated vegetation, have bee n subjected to realistically simulated precipitation with or without e nhanced N. The control 'rainfall' solute composition was appropriate f or the site of microcosm collection. In addition, N treatments were ap plied by adding to this basic mixture two or six times the ambient N d eposition for the site, as either (NH4)(2)SO4 or HNO3. For both Callun a-dominated and grass-dominated microcosms, the treatments over 12 mon ths resulted in significant falls in peat C:N ratio, associated with s ubstantial increases in exchangeable NH4+. The accumulation of NH4+-N in peat was greater under Calluna than under grass for all N treatment s. Peat KCl-extractable NH4+ concentration increased significantly wit h increasing (NH4)(2)SO4 treatments under both types of vegetation. Ho wever, peat total N concentration was only increased significantly by both NH4+ treatments under Calluna and by the highest NH4+ treatment u nder grass. The results show that peat-based ecosystems respond rapidl y to enhanced N deposition, with NH4+-N deposition resulting in greate r soil N accumulation than the corresponding amount of NO3--N depositi on.