CHAPTER 4: THE TERRESTRIAL ENVIRONMENT 4.1 Life on Land Imposes Unique Constraints
Desiccation
o Greatest constraint imposed by terrestrial environments
Air is less dense than water
o Results in lower drag (frictional resistance) on movement of organisms
o Increases constraint imposed by gravitational forces
o Another constraint in terrestrial environments
Diffusion
o Process where water readily evaporates from the surfaces of cells
o Doesn’t happen if air is saturated with moisture Water Balance
o Balance of water between organisms and their surrounding environment
o Major factor in evolution of life on land
- Adaptations of plants:
o Aerial parts of most plants Stems and leaves are
coated with a waxy cuticle
Prevents water loss Waxy cuticle prevents
gas exchange Terrestrial plants have pores on surface (stomata) that allows gases to diffuse - Terrestrial Animals
o Acquire water through eating/drinking
- Terrestrial Plants
o Passive process of acquiring water
Kelp Forests
o Grows in dense stands o Anchored to the bottom
sediments
o Afloat by gas-filled bladders attached to each blade Temperature & Moisture
o Short – term effect on Metabolic Processes
o Long – term influence on evolution and distribution of plants and animals
4.2 Plant Cover Influences the Vertical Distribution of Light
Vertical Gradient of Light
o Affected by absorption and reflection of solar radiation by plants
Leaves
o Affect light that comes in
o Shape of leaves and orientation affect it
o Measure of leaves would be Leaf Area Index
m2 leaf area / m2 ground area
the greater the LAI, the lower the quantity of light reaching that surface LAI increases as you
move from the canopy to the ground of the forest Beer’s law
Describes
relationship of Light and LAI
Photosynthetically Active Radiation (PAR)
o Wavelengths used by plants as a source of energy in
photosynthesis
o Varies through plant canopy o Visible light (400 – 700 nm) o Transmittance of PAR is less
than 10%
o Transmittance of Far-Red Radiation (730 nm) is greater
Ratio of red to far-red radiation decreases through canopy This shift in spectral quality of light affects production of Phytochrome Phytochrome
o Pigment that allows a plant to perceive shading by other plants o Influences patterns of growth
and allocation Angle of Leaf
o Affects amount of light it absorbs
o Perpendicular Leaf
Absorbs 1 unit of light energy (per unit leaf area/time)
o 60 degree leaf 0.5 units
o Angle of leaf may affect in various forms depending on location
High-Latitude environments
Sunlight angles are low; canopies displayed at angle will absorb more light
Tropical Areas
Angled leaves are also ideal to reduce great water loss in the afternoon Seasons may also affect the Leaf Area
o Dry Season
Increased light availability at ground level
o Spring
Leaves are just
expanding, incoming light in forest floor greater 4.3 Soil is the Foundation upon Which All Terrestrial Life Depends
Soil
o Medium for plant growth
o Principal factor controlling fate of water
o Nature’s recycling system Breaks down waste
products of plants and animals
o Formal Definition
Natural product formed and synthesized by
Weathering of rocks
Action of living organisms Natural body of earth
composed of:
Mineral
Organic matter
Supports plant growth
o Accdg to Hans Jenny the Pioneer of modern Soil Studies (waw nerd alert hahah jk)
Soil is the Stratum below the vegetation and above hard rock
No formal definition o Soil is not abiotic since it has life Regolith
o Layer of unconsolidated debris over hard unweathered rock o Where soil is formed
4.4 Formation of Soil Begins With Weathering Soil Formation
o Begins with weathering of rocks and minerals
o Weathering
Mechanical destruction of rock materials into
smaller particles as well as chemical modification Mechanical Weathering
o From interaction of several forces
o Combined action of wind, water and temperatures
Water freezes and cracks rocks
Wind wear away the surface
o Rock surfaces flake and peel away
o Break down into small particles Chemical Weathering
o Presence of water, oxygen and acids from organisms and organic matter
4.5 Soil Formation Involves Five Interrelated Factors
o Parent Material o Climate o Biotic factors o Topography o Time Parent Material
o Material from which soil develops
o May originate from:
Underlying bedrock Glacial deposits (till) Sand/silt carried by wind
(eolian)
Gravity moving down a slope (colluvium)
Sediments carried by water (fluvial)
Biotic Factors
o Plants, animals, bacteria and fungi
o Plant roots
Break up parent material, reduce erosion etc
Climate
o Temperature is a big deal when dealing with soil
o Heat can speed up reaction and breakdown etc etc
o Leaching
Movement of solutes through soil
Affected by temperature, precipitation and winds Topography
o Steep Slopes
More water runs off and less enters the soil Subject to soil erosion Time
o Time heals all… except for soil nagweweather lang hahahaha 4.6 Soils have certain Distinguishing
Physical Characteristics Color
o Easily defined and useful characteristic
o Things That Affect Color Organic Matter Makes soil dark/black Eg. Humus Oxides of Iron Color from yellowish-brown to red Manganese Oxides Purplish to black color
Quartz, Kaolin, Gypsum & Carbonates of Calcium & Magnesium
Whitish and grayish color
Poorly Drained Soil/ Soils with Saturation by water
Yellowish – brown and gray
o Munsell Soil Color Chart
Standardized Color Chart Texture
o Proportion of different-sized soil particles
o Inherited from parent material o Particles classified based on size
as:
Gravel (particles larger than 2.0mm)
Sand (0.05 mm to 2.0 mm)
Silt (0.002 to 0.05mm) Clay (less than 0.002 mm)
Most water-holding capacity
Exchange of ions o Affects pore space in soil
Plays role in movement of air and water in soil
Finer texture, smaller pores, greater availability of water adhesion and chem.. activity
Depth
o Depends on slope, weathering, parent materials and vegetation o Grasslands
Tend to be several meters deep
Soil from deep fibrous roots
o Forests
Shallow soil
o Alluvial Plains and Slopes Deep
4.7 Soil Body has Horizontal Layers or Horizons
Soil Profile
o Sequence of Horizontal Layers (horizons) Easily visible 4 Horizons o O Horizon Organic Layer Subdivided into: Oi o Surface layer of decomposing twigs and leaves Oe o Middle layer of decomposing plant tissues Oa
o Bottom layer of dark brown to black
homogenous organic material
o Aka the Humus Layer Thinnest in summer (cos
of decomposition) and thickest in fall
o A Horizon Topsoil
Mineral soil from organic matter (Humus)
Downward movement of water resulting in loss of minerals and finer soil particles sometimes gives rise to E Horizon
Layer of maximum leaching/eluviations Usually in forests, rarely in grasslands o B Horizon Subsoil
Less organic matter than A Horizon
Denser than A Horizon o C Horizon
Unconsolidated Layer Original material from
which soil was developed Below the C Horizon is the
Bedrock
4.8 Moisture – Holding Capacity is An Essential Feature of Soils
Size of Soil Particles & Spacing
o Determine how much water can flow in
Saturated Soil
o More water than pore space can hold
o Excess water drains freely from soil
Field Capacity
o Water fills all pore spaces held there by internal capillary forces o Expressed as % weight or
volume of soil occupied by water when saturated
Capillary Water
o Water held between soil particles by capillary forces
Clay
Small pores, holds more water
Sandy Soil
Large Pores, water drains quickly Wilting Point
o Moisture level decreases to a point where plants can no longer extract water
Available Water Capacity (AWC)
o Amount of water retained by soil between Field Capacity and Wilting Point
Field capacity and wilting point heavily affected by soil texture
o Highest in clay loam soils Topography affects moisture
o Water drains downslope o Higher slopes dry
4.9 Ion Exchange Capacity is Important to Soil Fertility Ion o Charged particle o Cations Positive charge In soil (Mg2+ , Ca2+, NH4 + ) o Anion Negative charge In Soil (NO3 - , SO4 2- ) Ion Exchange Capacity
o Total Number of Charged Sites on Soil Particles within a Volume of Soil
Ability of ions to bind on surface of soil depends on charged sites
Colloids
o Negatively charged particles in the soil prevalent in temperate zones (why cation exchange dominates the area)
Cation Exchange Capacity
o Total number of negatively charged sites located on edges of clay particles and humus o Negative charge enable soil to
prevent leaching of positively charged cations
o Fewer negatively charged sites in soil
Nitrate and phosphate (both anions) are not retained
Smaller the ion, the greater its positive charge, the more tightly it is held Lyotropic Series of Major Cations
according to their strength of bonding to the cation exchange sites
o Al3+ > H+ > Ca2+ > Mg2+ > K+ = NH4+ > Na+
o Higher conc of soil can
overcome these affinities in this series
More Hydrogen makes the soil acidic o More Al3+ also means the soil is
acidic (toxic to plants)
Result is reduced nutrient uptake
o More than pH 7 = Basic o Less than pH 5.6 = Acidic 4.10 Basic Soil Formation Processes
Produce Different Soils Pedogenesis
o Soil formation
5 Processes that give rise to the different classes of soil
o Laterization o Calcification o Salinization o Podzolization o Gleization Laterization
o Soils in humid environments o Tropical/subtropical regions
o Rainy conditions cause rapid weathering
o Movement of water causes heavy leaching
Leaching causes loss of cations; making it acidic o Most nutrients not taken up by
plants
Except for Iron and Aluminum
Iron Oxide o Give red
color Calcification
o Evaporation and water uptake exceed precipitation
o Result is upward movement of alkaline salts, specifically (CaCO3) o Infiltration of water Causes downward movement of salts Deposition and buildup of B Horizon (Subsoil) o Deposits may form hard layer called Caliche Salinization
o Similar to calcification except it is in drier climates
o Salt deposits occur near soil surface
Podzolization
o In cool, moist climates o In coniferous vegetation o Organic matter creates acidic
condition
Acidity removes cations (iron and aluminum) in topsoil
Creates sub layer from A Horizon of white to gray colored sand Gleization
o in high rainfall but poor drainage (waterlogged)
o constantly wet conditions slows breakdown of organic matter by decomposers
allows matter to build up in top layer
reacts with iron to form black to bluish – gray color
eg. Gelisol
