Nitrogen is a key element in ecosystem processes. Aspects of local and global changes in nitrogen in both undisturbed and disturbed conditions are discussed. Environmental changes caused by pollution from nitrogenous compounds and changes in landuse are also described. Organisms, plants, animals and microorganisms are all affecting nitrogen supply. Emphasis is placed on natural and anthropogenic transfer of nitrogen between ecosystems and also on the interaction of nitrogen with other bioelements.

Inhalt

1 Introduction: Geochemical Occurrence of Nitrogen. Natural Nitrogen Cycling and Anthropogenic Nitrogen Emissions.- 2 Nitrogen in Plants and Soils: Physiological and Microbiological Background for Biological Nitrogen Turnover.- 2.1 Nitrogen in Plants.- 2.2 Nitrogen in Soils: Transformations, Uptake, Losses.- 2.2.1 Organic Matter Decomposition, Nitrogen Mineralization to Ammonium Ions, Microbial Immobilization and Root Uptake.- 2.2.2 Nitrification.- 2.2.3 Denitrification: A Homeostatic Mechanism?.- 2.2.4 Nitrogen Fixation.- 2.3 Nitrogen and Transport Mechanisms in Terrestrial Ecosystems.- 2.3.1 Within-Site-Transfers.- 2.3.2 Inputs to and Outputs from Terrestrial Ecosystems.- 3 Nitrogen-Limited and Nitrogen-Depleted Terrestrial Ecosystems: Ecological Characteristics.- 3.1 Definitions.- 3.2 Nitrogen in Forest Successions.- 3.3 Biological Control of Nitrogen Cycling.- 3.4 Nitrogen Depletion by Fire and Other Disturbances.- 3.5 Nitrogen Depletion by Removal of Biomass or Litter.- 3.6 Concluding Remarks.- 4 Nitrogen-Enriched and Nitrogen-Saturated Ecosystems.- 4.1 Definitions.- 4.2 Sites Naturally Enriched with Nitrogen.- 4.3 Nitrogen Enrichment by Preindustrial Agricultural and Pastural Land Use.- 4.4 Enrichment by Chemical Fertilizers and Urban Waste Products.- 4.5 Enrichment by Atmospheric Emissions from Modern Industrial and Agricultural Activities.- 5 Consequences of Increased Nitrogen Supply to Forests and Other Natural and Seminatural Terrestrial Ecosystems.- 5.1 Changes in Vegetation and Fauna.- 5.1.1 Forest Vegetation.- 5.1.2 Grasslands, Heathlands, and Wetlands.- 5.1.3 Fauna.- 5.1.4 Discussion.- 5.2 Soil Chemical and Biological Changes, Including Nitrogen Losses to Groundwater and Atmosphere.- 5.2.1 Factors Affecting Biological Activity in Soils with Differences in Nitrogen Supply.- 5.2.2 Consequences of Increased Nitrogen Supply.- 5.3 Acute Damage to Plants Associated with Emissions of Nitrogen Compounds.- 5.3.1 Damage Caused by NOx or HNO3.- 5.3.2 Damage Caused by Photochemical Oxidants, in Particular Ozone.- 5.3.3 Damage Associated with Gaseous Ammonia.- 5.3.4 Damage to Roots Associated with Nitrification-Caused "Acid Surges" in Soil.- 5.3.5 Damage by Climatic Stress Aggravated by Increased Sensitivity in Nitrogen-Rich Plants.- 5.3.6 Damage by Grazing Animals or Pests, Associated with Changes in Palatability or Chemical Defense.- 5.4 Interactions Between Effects of Anthropogenic Nitrogen Emissions and Other Human Impacts on Terrestrial Ecosystems.- 5.4.1 Changes in Land Use.- 5.4.2 Management Impacts on Forest Ecosystems Enriched with Nitrogen.- 5.4.3 Interactions Between Deposition of Nitrogen and Other Air Pollutants.- 6 Conclusions.- References.