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Title Impacts of nitrogen deposition on plant physiological parameters controlling the ammonia compensation point. Annual report.CEH Staff publications
Name(s) Sutton, M A (Mark)
Hill, P W
Fowler, D. (David)
Raven, J A
Institute of Terrestrial Ecology
Physical Details 10pp.
Publication 1996
Subjects T07059b5; CEH staff publication;
Files CEH Staff copy
Abstract The 'umbrella' work at lTE Edinburgh on the effects of N deposition on semi-natural ecosystems is considering the effects of inputs of nitrogen on both species composition change and plant physiological indicators. This short report describes the progress on the latter component, which is focused on the impacts of elevated nitrogen on the ammonia compensation point of semi-natural species. Increased nitrogen deposition, both as oxidized and reduced nitrogen is known to increase the nitrogen content of the foliage of both semi-natural higher plants and mosses. Although measurements are currently absent, it is also expected that increased nitrogen deposition will increase the concentrations of ammonium plant intercellular (apoplastic) fluids. 'In the absence of any parallel changes in apoplastic pH, this will raise the gaseous ammonia concentration at equilibrium with the plant tissues; net ammonia deposition will be reduced and the potential for ammonia release from semi-natural plants increased. Information on these relationships is important to establish the extent of impacts of atmospheric nitrogen deposition 011 plants and their underlying physiology. It is expected that the apoplastic ammonium concentrations and compensation point may be used as indicators of atmospheric nitrogen deposition, while in addition this provides important data for models linking net ammonia exchange to impacts. The first year of work has been concerned with the development of two independent approaches to estimate compensation points for a semi-natural species, Luzula sylvatica (Woodrush): I) Direct measurement of apoplastic pH and ammonium as a plant bioassay. II) Controlled gas exchange measurements of ammonia, CO2 and H2O. The work so far has developed the systems for both approaches and provided initial bioassay and gas exchange determinations of the compensation point for this species. A range of treatments has been put in place for growing a large number of replicates of Luzula
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