Nitrogen in Terrestrial Ecosystems

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.