Photosynthesis

• Light absorption occurs in the thylakoid membranes of chloroplasts.
• Defining soil


  Basic approaches
• There is no officially accepted definition for soil
• Approaches to defining soil

  • Composition
  • Particle size distribution
  • Presence of soil forming factors and processes
  • Ability to provide essential ecosystem services
• Narrowing down soil definition to a small number of properties is too simplistic
• Particle size


  An example of a simplistic approach that does not capture all aspects of soil
• Soil definition of Certini and Ugolini (2012): "Soil is a centimetric or thicker unconsolidated layer of fine-grained mineral and/or organic material, with or without coarse elements and cemented portions, lying at or near the surface of planets, moons and asteroids, which shows clear evidence of chemical weathering"
• Soil definition by Certini and Ugolini (2012)

  • Centrimetric or thicker
  • Unconsolidated layer
  • Consisting of fine-grained minerals
  • With or without coarse elements
  • With or without cemented portions
  • Shows clear evidence of chemical weathering
• Limitations of the soil definition by Certini and Ugolini (2012): Does not include if the presence of life is needed or if it should be a functional component of the ecosystem
• Soil is a good fit for life due to small particles creating large surface area and internal open spaces
• Soil provides a moderated environment even under harsh conditions like deserts
• Soil blocks out harmful UVB radiation


  Soil can block out even the most dangerous UV radiation - UVC
• Soil protects against solar radiation and is a poor conductor of heat
• Soil retains water and decreases the propensity of water to change phase
• All mineral surfaces in soil carry charge and impart chemical reactivity
• Soil promotes the establishment of micro-organisms like cyanobacteria
• Cyanobacteria fix nitrogen from the atmosphere and photosynthesize
• Soil accelerates the weathering of rocks
• Secondary clay minerals have been identified on Mars
• Properly functioning soils translate to food security on Earth
• Combination of soil functions give ecosystem services
• Soil threats


  • Erosion
  • Soil carbon loss
  • Nutrient imbalances
  • Loss of soil biodiversity
  • Soil acidification
  • Soil compaction
  • Urban expansion (surface sealing)
  • Soil pollution
  • Soil salinisation
  • Waterlogging
• Human activities alter spatial distribution of nutrients

  Nutrient imbalances
• Soil acidification is caused by human activity

  It is a chemical degradation of soil
• Soil compaction is caused by human activity

  • It is a physical degradation of soil which increases run-off
  • Soil holds less water and exhibits poor aeration
  • It occurs in agriculture, mining, and urban environments
• Urban expansion (surface sealing)

  • More soil surfaces are covered by roads, pavement, and buildings
  • Soils are disconnected from the rest of the environment
  • Cannot perform any ecosystem services
• Soil pollution


  • The introduction and accumulation of non-essential and toxic elements or compounds
  • For example, lead, mercury
  • Essential elements can also accumulate to levels toxic for life
• Soil salinisation


  • The accumulation of salts in soil to levels detrimental for life
  • Can occur in poorly managed irrigation schemes
• Waterlogging


  • In some areas of the world, the logging of forests and savannah trees result in increasing water tables
  • In Western Australia, for example, the rising water table is saline
  • In an urban environment, all the run-off water from built-over soil must report somewhere
• Possible impacts of various soil impacts

  • Loss of soil biodiversity
  • Soil acidification
  • Soil compaction
  • Urban expansion (surface sealing)
  • Soil pollution
  • Soil salinisation
  • Waterlogging
• Soil functions are under threat
• Are cities net accumulators of nutrients
• Soil is an important sink and source of nutrients
• Decomposition of organic matter

  Recycling nutrients and organic waste
• Functions of soil


  • Engineering medium
  • Growth medium for plants
  • System for recycling nutrients and organic waste
• Man has utilised soil as a building and engineering medium for millennia
• The vast majority of plants cannot survive or reproduce without soil
• About 10,000 years ago, man realised the potential of crop cultivation and the utilisation of soil as a growth medium for plants
• Since the advent of ancient agriculture, the survival of the human race has been intimately linked with the soil and its sustainable management
• The world's first civilisation in Sumer collapsed in 2370 B.C. due to unsustainable soil cultivation that resulted in soil salinisation