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
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
