Chapter 4 Terrestrial Environment

CHAPTER 4: THE TERRESTRIAL ENVIRONMENT

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4.1 Life on Land Imposes Unique Constraints

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 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

Short – term effect on Metabolic Processes 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

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 o

4.3 Soil is the Foundation upon Which All Terrestrial Life Depends  Soil o o o

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Medium for plant growth Principal factor controlling fate of water Nature’s recycling system  Breaks down waste products of plants and animals Formal Definition  Natural product formed and synthesized by  Weathering of rocks

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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  5 Factors of Soil Formation

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Parent Material Climate Biotic factors

 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

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Topography Time 

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

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Forests  Shallow soil 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 C Horizon  Unconsolidated Layer  Original material from which soil was developed  Below the C Horizon is the Bedrock 

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 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

Cations  Positive charge  In soil (Mg2+ , Ca2+, NH4 + )

 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

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Laterization Calcification Salinization

 Laterization o Soils in humid environments o Tropical/subtropical regions

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 o

 4.9 Ion Exchange Capacity is Important to Soil Fertility  Ion o

Charged particle

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Anion  Negative charge  In Soil (NO3 - , SO4 2- )

 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 o

Podzolization Gleization

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Rainy conditions cause rapid weathering

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

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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 

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