Book contents
- Frontmatter
- Contents
- Preface
- 1 Introduction
- 2 Soil properties
- 3 Forest soil development and classification
- 4 Soil fungi
- 5 Soil water
- 6 Forest carbon cycle
- 7 Nutrient cycling
- 8 Northern forests in a high-CO2 world
- 9 Soil acidity and heavy metal pollution
- 10 Nitrogen
- 11 Soil functioning and climate change
- References
- Index
- Plate section
10 - Nitrogen
Published online by Cambridge University Press: 26 April 2011
- Frontmatter
- Contents
- Preface
- 1 Introduction
- 2 Soil properties
- 3 Forest soil development and classification
- 4 Soil fungi
- 5 Soil water
- 6 Forest carbon cycle
- 7 Nutrient cycling
- 8 Northern forests in a high-CO2 world
- 9 Soil acidity and heavy metal pollution
- 10 Nitrogen
- 11 Soil functioning and climate change
- References
- Index
- Plate section
Summary
Nitrogen cycle
Nitrogen is an essential plant macronutrient, constituting a crucial component of both structural (e.g. lignin) and metabolic substances (e.g. enzymes). Plants' requirements for N are higher than for any other macronutrient; for example, the average concentration of N in plants is four times that of the next most common element, potassium. In many forest ecosystems N is, or should be, a factor limiting growth. However, this situation has changed in the past 150 years with advent of N inputs from air pollution and agriculture. Before industrialisation, new N inputs into ecosystems were derived from atmospheric deposition and biological fixation, but the relative importance of these sources has changed rapidly.
Before industrialisation, biological nitrogen fixation was the major source of N into ecosystems. In forests N is fixed biologically by a number of organisms, including trees, mosses and soil blue-green algae. Atmospheric inputs were mainly from N fixation and from natural phenomena such as lightning, resulting in N inputs of 1–2 kg ha−1 yr−1. Today, even remote forest ecosystems may have elevated inputs of N. Total inorganic N deposition in or close to the centres of large industrial activity range from about 3 to 30 kg N ha−1 yr−1 in North America, 5–75 kg N ha−1 yr−1 in Europe and 8–40 kg N ha−1 yr−1 in China, far exceeding the natural deposition rate.
- Type
- Chapter
- Information
- Soil Ecology in Northern ForestsA Belowground View of a Changing World, pp. 195 - 212Publisher: Cambridge University PressPrint publication year: 2011