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Nitrogen Saturation of Terrestrial Ecosystems: Some Recent Findings and Their Implications for Our Conceptual Framework

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Water, Air, & Soil Pollution: Focus

Abstract

The consequences of nitrogen (N) enrichment for terrestrial and freshwater ecosystems are of increasing concern in many areas due to continued or increasing high emission rates of reactive N. Within terrestrial ecosystems various conceptual frameworks and modelling approaches have been developed which have enhanced our understanding of the sequence of changes associated with increased N availability and help us predict their future impacts. Here, some recent findings are described and their implications for these conceptual frameworks and modelling approaches discussed. They are: (a) an early loss of plant species that are characteristic of low N conditions as N availability increases and a loss of species with high N retention efficiencies (so called N ‘filters’), (b) suppression of microbial immobilisation of deposited \({\text{NO}}^{ - }_{3} \) due to increased \({\text{NH}}^{ + }_{4} \) availability in the early stages of N saturation, (c) the early onset of \({\text{NO}}^{ - }_{3} \) leaching due to these changes (a and b above) in both plant and microbial functioning, (d) reduced sensitivity of vegetation to N additions in areas with high historical N deposition, (e) delayed changes in soil C:N changes due to increased net primary productivity and reduced decomposition of soil organic matter. Some suggestions of early indicators of N saturation are suggested (occurrence of mosses; \({\text{NH}}^{ + }_{4} :{\text{NO}}^{ - }_{3} \) ratio in surface soils) which indicate either a shift in ecosystem function and/or structure.

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Acknowledgements

The UK Department of the Environment, Food and Rural Affairs and the Natural Environment Research Council provided the funding for many of the UK studies reported here and the time for this synthesis. My thanks to the Acid Rain 2005 Organising Committee for giving me the opportunity to share these ideas and to the many colleagues and two referees for their helpful comments.

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    Bridget A. Emmett

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Emmett, B.A. Nitrogen Saturation of Terrestrial Ecosystems: Some Recent Findings and Their Implications for Our Conceptual Framework. Water Air Soil Pollut: Focus 7, 99–109 (2007). https://doi.org/10.1007/s11267-006-9103-9

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