Accumulation of pollutant nitrogen in calcareous and acidic grasslands: Evidence from N flux and 15N tracer studies |
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Authors: | Gareth K. Phoenix Jonathan R. Leake David J. Read J. Philip Grime John A. Lee |
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Affiliation: | (1) Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield, S10 2TN, U.K. |
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Abstract: | Semi-natural calcareous and acidic grasslands are known to be sensitive to increased atmospheric N deposition. However, the fate of pollutant N within these systems is unknown. This paper reports on the first studies to determine the fate of added N within a calcareous and an acidic grassland subject to long-term simulated enhanced N deposition. Intact soil/turf cores were removed from field plots treated for six years with enhanced N deposition (ambient +0, +35 and +140 kg N ha–1 year–1). Cores were inserted into lysimeters and output fluxes of N were monitored in detail. Complete N budgets—calculated from the N flux data—showed considerable accumulation of N within the treated grasslands, up to 76% and 38% of pollutant N in the calcareous and acidic grasslands respectively. In the second study, the short-term (21 day) fate of pollutant N was determined by tracing 15N labelled ammonium nitrate (+35 kg N ha–1 year–1) though the acidic and calcareous lysimeters into plant, soil and leachate pools. Up to 91% and 59% of 15N was recovered in soils and vegetation of the calcareous and acidic grasslands respectively, with negligible amounts recovered in soil extractable ammonium and nitrate (<0.3%) and in leachate (<0.02%). This rapid short-term immobilisation of pollutant N supports the long-term accumulation of the element calculated from the N flux study. |
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Keywords: | 15N stable-isotope pulse-chase denitrification ecosystem N budgets immobilisation leachate N deposition N fluxes pollutant N accumulation volatilization |
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