Carbon and nitrogen cycling

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Carbon and nitrogen cycling

• Dr Wendy Seel
• Department of Plant Soil Science

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Key resources for the living world

• CARBON
• 45 of dry matter
• Derived from the atmosphere
• NITROGEN
• 1-3 of dry matter
• Derived from the atmosphere

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How are carbon and nitrogen captured?

• CARBON
• 0.04 of the atmosphere
• fixed by green plants during PHOTOSYNTHESIS
• NITROGEN
• 79 of the atmosphere
• fixed by bacteria, either free-living or in
  association with plants

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Carbon and nitrogen are FINITE resources

• Energy from the sun is in infinite supply, but
  cannot be recycled
• Material resources are in finite supply, but can
  recycled
• Time scales can be lengthy!

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What is the carbon cycle?
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What is the nitrogen cycle?
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Why are carbon and nitrogen cycles of interest to
man?

• The population increases by 250 people every
  minute!
• The production of FOOD and materials is essential
• C N cycles affect PRODUCTIVITY

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What is productivity?

• The rate or efficiency of work
• Industrial e.g. number of cars assembled per
  unit investment per unit time
• Biological Biomass produced per unit area per
  unit time

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What roles do organisms play in productivity?

• Primary producers
• plants
• photosynthetic bacteria
• Secondary producers
• herbivores
• Tertiary producers
• Carnivores
• Decomposers

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Is productivity uniform across the globe?

• Net Primary Productivity on land
• 120 x 109 tonnes dry weight per year
• Net Primary Productivity in the oceans
• 60 x 109 tonnes dry weight per year

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Is productivity uniform on land?
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What limits productivity?

• RESOURCES
• Irradiance
• Water
• Nutrients
• CONDITIONS
• Temperature
• Pests and diseases

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Irradiance

• Irradiance - the number of photons incident on an
  area during a period of time
• Plants cannot use the entire spectrum
• useable wavelengths 400-700 nm

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Irradiance cont.

• Reciept of irradiance is not constant during time
  and space
• shading
• patchiness
• seasons

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Water

• Water is part of photosynthesis and is a medium
  for photosynthesis
• Water helps regulate leaf temperature
• Water is needed to support cell structure and
  growth
• Water helps supply nutrients

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Nutrients

• Nutrients are used to make and operate essential
  components of living things
• Nutrients directly affect productivity
• Nutrients can be supplied and removed by water

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Temperature

• Photosynthesis is temperature dependent
• Respiration is temperature dependent

Increasing Temperature
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Global environmental change

• Global warming
• Changing weather patterns
• Pollution of land and water
• Deforestation, desertification and salinisation
• Genetic modification

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International Biological Programme

• The biological basis of human welfare
• Knowledge needed for rational resource management
• Is it too late?