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Title: Effect of nitrogen enrichment on the ecology and nutrient cycling of a lowland heath
Author: Wilson, Deirdre Barnetson.
Awarding Body: Manchester Metropolitan University
Current Institution: Manchester Metropolitan University
Date of Award: 2003
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This study was part of an ongoing investigation into the long-term effects of nitrogen enrichment and environmental stress on lowland heath ecology and nutrient cycling. The original experimental site, 4 replicate blocks of 2m x 1m plots, was established on pioneer-phase Calluna vulgaris - Deschampsia flexuosa heathland in 1996 (Cawley, 2000). Nitrogen treatments (0, 20, 60 & 120 kg N ha" yr") have been applied on a fortnightly basis, against a background deposition of -20 kg N ha'! yr" (NOx & NHy). During 1997 the plots were split and a six-month drought versus non-drought treatment introduced (full details in Cawley, 2000). The period of environmental stress experienced by the dominant C. vulgaris canopy was extended over the following two years (1998 & 1999) by a natural outbreak of Lochmaea suturalis. Zero-tension lysimeters were installed under the non-droughted half of these plots (2001), facilitating study of increased nitrogen deposition effects upon nitrogen losses through leaching.' A second set of experimental plots were started in 2000 to enable study of germination and establishment of D. flexuosa under conditions of increased nitrogen deposition and canopy gap creation in an otherwise closed C. vulgaris canopy. This study has shown that elevated, long-term deposition of atmospheric nitrogen in combination with periods of environmental stress can contribute to significant changes in the ecology and nutrient cycling of a lowland heath. Elevated nitrogen deposition was found to induce significant increases in: tissue nitrogen content of Calluna and Hypnum sp.; litter nitrogen content; the loss of nitrogen from the system through leaching. Additionally, there were significant reductions in the C/N ratio of both vegetation and soil. This could have major implications for changes in the rates of nitrogen mineralisation and immobilisation in this nitrogen-limited ecosystem. By 2001, few effects of the 1997 drought continued to be apparent in the heathland vegetation. However differences were recorded in the nitrogen content and C/N ratio of the soil components of the droughted and nondroughted plots. Some responses were not as expected, such as the transitory increase in the Deschampsia population. The predicted outcome, based on studies of other European lowland heaths, would have been for a marked transition to a Deschampsia-dominated canopy, especially in those high nitrogen (80N & 140N) treatment plots which had been droughted in 1997. Nitrogen deposition levels in excess of the critical load for dry heathlands (10 - 20 kg N ha" yr"), in combination with Calluna canopy opening induced by environmental stress, have been associated with such transitions in vegetation on Continental heaths. An equally unexpected outcome of this study was the significant recovery of the moss layer after the cessation of drought conditions in 1997. Again, reports from other European heaths have suggested that increased nitrogen deposition would normally be associated with a loss of bryophytes and cryptograms. Elevated nitrogen inputs, at this study site, have been associated with a reduction in bryophyte species diversity. Conversely, there has been a corresponding, significant, increase in the cover of nitrophilic Hypnum species.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Ecology Ecology Air Pollution Air Pollution