BIOL 4120: Principles of Ecology Lecture 5: Terrestrial Environment

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BIOL 4120 Principles of Ecology Lecture 5
Terrestrial Environment

• Dafeng Hui
• Office Harned Hall 320
• Phone [phone]
• Email dhui_at_tnstate.edu

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• Topics for this class
• 5.1 Soil is the foundation of all life
• 5.2 Formation of soil
• 5.3 Physical properties of soil
• 5.4 Soil horizons
• 5.5 Soil water holding capacity
• 5.6 Soil ion exchange capacity
• 5.7 Soil classification
• 5.8 Light distribution in plant canopy

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5.1 Soil is the foundation upon which all
terrestrial life depends

• Before life invaded the land from the sea, there
  was probably little that looked like soil today
• Dust like Mars Little organic matter
• A few microorganisms.
• Soil is medium for plant growth the basis of all
  terrestrial life. Without soil, there would be no
  plants, no soil microorganism and no land animals
• Plants obtain many of their water and nutrients
  from soil and it provides an place to attach to.

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Definition of soil

• Soil is hard to define because it is so complex
• Soil is a natural product formed and synthesized
  by the weathering of rocks and the action of
  living organism.
• Soil is a collection of natural bodies of earth,
  composed of mineral and organic matter and
  capable of supporting plant growth.
• The stratum below vegetation and above hard rock

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• Soil is a living system made up of a three
  dimensional matrix (length, width, and depth) and
  of minerals and organic matter, and organisms
• plants, both roots and stems
• Bacteria
• Fungi
• Algae
• Small animals
• Larger animals

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5.2 Formation of soil

• Starting Point weathering of rocks and their
  minerals.
• Mechanical and Chemical Weathering
• Mechanical interaction of several forces
• Water
• Wind
• Temperature
• Creates loose material
• Sorted and moved
• Chemical
• Acids produced by lichens and mosses
• Addition of organic matter (dead plants and
  animal tissues)
• Oxidization
• etc

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Five interrelated factors

• Five factors are involved in the formation of
  soil
• Parent Material
• Igneous rock
• Sedimentary rock
• Metamorphic rock
• Climate
• Temperature Rainfall
• Wind Elevation
• Latitude
• Biotic Factors
• Living organisms (plants, animals, bacteria,
  fungi).
• Degradation by living organisms
• Topography
• Water runoff
• Draining
• Erosion
• Time
• Weathering, accumulation, decomposition and
  mineralization take time
• Initial differentiation can be within 30 years

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5.3 Soils show a great deal of variation

• Color
• No direct effect on how soil function
• Allows classification
• Red
• Possibly oxides
• Black
• Possible high organic content
• Texture
• Variation in size and shape of soil particles
• Gravel
• gt2mm
• Sand
• 0.05mm to 2mm
• Silt
• 0.002mm to 0.05mm
• Clay
• lt0.002mm

Soil texture is percentage of sand, silt and
clay. (Texture chart)
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• Structure
• Space for roots etc
• Pore space
• Amount of water held
• Rate of water movement
• Aeration
• Compaction
• Aggregation
• Depth
• Depends on
• Slope
• Weathering
• Parent material
• Vegetation
• Grasslands are deep
• Forests are shallow

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5.4 Soil has horizontal layers
Soil profile Layers or horizons
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5.5 Moisture holding capacity is an essential
feature of soils

• Soil can become saturated if all pores filled
• All water is hold by soil particulars, at field
  capacity (FC)
• Capillary water is usually present
• Extracted by plants
• Wilting point (WP)
• Plant no long extract water
• Available water capacity (AWC)
• All affected by soil texture
• Sand
• Lower capacity
• Clays
• Higher capacity

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Water content at different soils
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5.6 Ion exchange capacity is important to soil
fertility

• Soil soluble nutrients are charged particles,
  ions.
• Cations positively charged (Ca2, Mg2, NH4)
• Anions negatively charged (NO3, PO34)
• Ions are attached to soil particles, so do not
  leach out of the soil.
• Ion exchange capacity total number of charged
  sites on soil particles in a standard volume of
  soil.

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Soils have an excess of negative charged sites

• Cationic exchange dominant (colloids)
• Cation exchange capacity (CEC) total of
  negatively charged sites, located on the leading
  edges of clay particles and SOM.
• Concentration and affinity

Al3 gt H gt Ca2 gt Mg2 gt K NH4 gt Na
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Soils have an excess of negative charged sites

• Change in pH affects binding capacity for ions
• Immovable
• Hydrogen (H)
• Aluminum (Al)
• Removable in order
• Calcium (Ca)
• Magnesium (Mg)
• Potassium (K)
• Ammonium (NH4)
• Sodium (Na)

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Process of cation exchange in soils
In soils with high Mg or Ca, K is lacking,
why?
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5.7 Basic Soil Formation Processes Produce
Different Soils

• Regional differences in geology, climate, and
  vegetation give rise to characteristically
  different soils
• The broadest level of soil classification is soil
  order

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• There are twelve orders of soil

• Entisol
• Mollisol
• Alfisol
• Andisol
• Aridisol
• Inceptisol

• Histosol
• Oxisol
• Vertisol
• Spodosol
• Ultisol
• Gelisol

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5.7 Soils vary with climate and vegetation
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Ultisols

• Ultisol
• Warm climate soil
• Redish or yellowish
• Low nutrient content
• Laterization when PPT greatly exceeds ET in warm
  climates, water rapidly percolated through soil
  and into groundwater. Soluble soil nutrients are
  constantly leached out of soils, leaving behind
  the less soluble ions (Al and Fe) which give
  soil color (whitish for Al and red for Fe) and H
  make soil acidic and nutrient poor.

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Salinization (Aridisol)

• Salinization in very dry climates and when loss
  of soil moisture due to ET exceeds PPT, water
  leaves the soil through the surface. The minerals
  (NaCl) dissolved move upward from the groundwater
  and result in a salt crust on the surface of the
  soil.
• Irrigation of dryland can result salinization.
  This becomes a problem in US southwest,
  Australia, Northern Africa, China, and major
  areas of dryland irrigation.

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5.8 Light distribution within plant canopy

• Influencing factors
• Vegetation types
• Leaf area index (LAI)
• Leaf angles

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• Plant cover dramatically changes the light
  environment underneath it
• types of plants making up the cover can have an
  effect (small portion reach ground)
• Deciduous forest 1 to 5
• Coniferous forest 10 to 15
• Tropical rain forest 0.25 to 2

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Total LAI315/78.54
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• Effect of leaf angle on leaf area index and light
  penetration

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• Season also affects the light penetration
• The ground under a deciduous forest will undergo
  a seasonal cycle affected by leaf loss
• The ground under a coniferous forest will undergo
  a seasonal cycle unaffected by leaf loss
• The ground under a tropical rainforest will
  neither have a seasonal cycle or an effect from
  leaf drop

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Quantifying Ecology Beers Law and the
Attenuation of Light

• The greater the surface area of leaves, the less
  light will penetrate the canopy and reach the
  ground
• The attenuation (vertical reduction) of light
  through a stand of plants is estimated using
  Beers law

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Beers Law
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The End
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Basic Soil Formation Processes Produce Different
Soils

• Laterization is a process common to soils found
  in humid environments in the tropical and
  subtropical regions ? heavy leaching of nutrients
• Calcification occurs when evaporation and water
  uptake by plants exceed precipitation ?
  deposition and buildup of alkaline salts (CaCO3)
  in the subsoil
• Salinization occurs in very dry climates or
  coastal regions as a result of salt spray ? salt
  deposits near the soil surface

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• Podzolization occurs in cool, moist climates
  where coniferous vegetation (pine forests)
  dominates ? acidic soil enhances leaching of
  cations, iron, and aluminum from the topsoil
• Gleization occurs in areas with high rainfall or
  in areas of poor drainage ? organic matter is
  slowly decomposed and accumulates in the upper
  layers of soil

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Padilla and Pngnaire (2007, Functional Ecology.
Mediterranean Woody seedling)