BIOL 4120: Principles of EcologyBIOL 4120: Principles of Ecology

Lecture 5: Terrestrial Lecture 5: Terrestrial EnvironmentEnvironment

Dafeng HuiDafeng Hui

Office: Harned Hall 320Office: Harned Hall 320

Phone: 963-5777Phone: 963-5777

Email: dhui@tnstate.eduEmail: dhui@tnstate.edu

Topics for this class:

5.1 Soil is the foundation of all life5.1 Soil is the foundation of all life5.2 Formation of soil5.2 Formation of soil5.3 Physical properties of soil5.3 Physical properties of soil5.4 Soil horizons5.4 Soil horizons5.5 Soil water holding capacity5.5 Soil water holding capacity5.6 Soil ion exchange capacity5.6 Soil ion exchange capacity5.7 Soil classification5.7 Soil classification5.8 Light distribution in plant canopy5.8 Light distribution in plant canopy

5.1 Soil is the foundation upon 5.1 Soil is the foundation upon which all terrestrial life dependswhich all terrestrial life depends

Before life invaded the land from the sea, Before life invaded the land from the sea, there was probably little that looked like soil there was probably little that looked like soil todaytoday• Dust like Mars; Little organic matterDust like Mars; Little organic matter• A few microorganisms.A few microorganisms.

Soil is medium for plant growth; the basis of Soil is medium for plant growth; the basis of all terrestrial life. Without soil, there would be all terrestrial life. Without soil, there would be no plants, no soil microorganism and no land no plants, no soil microorganism and no land animalsanimals

Plants obtain many of their water and Plants obtain many of their water and nutrients from soil and it provides an place to nutrients from soil and it provides an place to attach to.attach to.

Definition of soilDefinition of soil Soil is hard to define because it is so Soil is hard to define because it is so

complexcomplex• Soil is a natural product formed and synthesized Soil is a natural product formed and synthesized

by the weathering of rocks and the action of by the weathering of rocks and the action of living organism.living organism.

• Soil is a collection of natural bodies of earth, Soil is a collection of natural bodies of earth, composed of mineral and organic matter and composed of mineral and organic matter and capable of supporting plant growth.capable of supporting plant growth.

• The stratum below vegetation and above hard The stratum below vegetation and above hard rockrock

Soil is a living system made up of a Soil is a living system made up of a three dimensional matrix (length, three dimensional matrix (length, width, and depth) and of minerals and width, and depth) and of minerals and organic matter, and organisms:organic matter, and organisms:

• plants, both roots and stemsplants, both roots and stems• BacteriaBacteria• FungiFungi• AlgaeAlgae• Small animalsSmall animals• Larger animalsLarger animals

5.2 Formation of soil5.2 Formation of soil

Starting Point: weathering of rocks and their Starting Point: weathering of rocks and their minerals.minerals.

Mechanical and Chemical WeatheringMechanical and Chemical Weathering

Mechanical: interaction of several forcesMechanical: interaction of several forces• WaterWater• WindWind• TemperatureTemperature• Creates loose materialCreates loose material• Sorted and movedSorted and moved

ChemicalChemical• Acids produced by lichens and mossesAcids produced by lichens and mosses• Addition of organic matter (dead plants and animal Addition of organic matter (dead plants and animal

tissues)tissues)• OxidizationOxidization• etcetc

Five interrelated factorsFive interrelated factors Five factors are involved in the formation of soilFive factors are involved in the formation of soil

• Parent MaterialParent Material Igneous rockIgneous rock Sedimentary rockSedimentary rock Metamorphic rockMetamorphic rock

• ClimateClimate Temperature RainfallTemperature Rainfall Wind ElevationWind Elevation LatitudeLatitude

• Biotic FactorsBiotic Factors Living organisms (plants, animals, bacteria, fungi).Living organisms (plants, animals, bacteria, fungi). Degradation by living organismsDegradation by living organisms

• TopographyTopography Water runoffWater runoff DrainingDraining ErosionErosion

• TimeTime Weathering, accumulation, decomposition and mineralization take Weathering, accumulation, decomposition and mineralization take

timetime Initial differentiation can be within 30 yearsInitial differentiation can be within 30 years Formation of true soil, 2000 to 20000 yearsFormation of true soil, 2000 to 20000 years

5.3 Soils show a great deal of variation5.3 Soils show a great deal of variation ColorColor

• No direct effect on how soil No direct effect on how soil functionfunction

• Allows classificationAllows classification RedRed

• Possibly oxidesPossibly oxides BlackBlack

• Possible high organic Possible high organic contentcontent

TextureTexture• Variation in size and shape of soil Variation in size and shape of soil

particlesparticles GravelGravel

• >2mm>2mm SandSand

• 0.05mm to 2mm0.05mm to 2mm SiltSilt

• 0.002mm to 0.05mm0.002mm to 0.05mm ClayClay

• <0.002mm<0.002mm

Soil texture is percentage of sand, silt and clay. (Texture chart)

StructureStructure• Space for roots etcSpace for roots etc• Pore spacePore space

Amount of water heldAmount of water held Rate of water movementRate of water movement AerationAeration CompactionCompaction AggregationAggregation

DepthDepth• Depends onDepends on

SlopeSlope WeatheringWeathering Parent materialParent material VegetationVegetation

• Grasslands are deepGrasslands are deep• Forests are shallowForests are shallow

5.4 Soil has horizontal layers5.4 Soil has horizontal layers

Soil profile

Layers or horizons

5.5 Moisture holding capacity is an essential 5.5 Moisture holding capacity is an essential feature of soilsfeature of soils

Soil can become saturated if Soil can become saturated if all pores filledall pores filled

All water is hold by soil All water is hold by soil particulars, at field capacity particulars, at field capacity (FC) (FC)

Capillary water is usually Capillary water is usually present present • Extracted by plantsExtracted by plants

Wilting point (WP)Wilting point (WP)• Plant no long extract waterPlant no long extract waterAvailable water capacity Available water capacity

(AWC)(AWC)

All affected by soil textureAll affected by soil texture• Sand Sand

Lower capacityLower capacity• ClaysClays

Higher capacityHigher capacity

Water content at different soilsWater content at different soils

5.6 Ion exchange capacity is 5.6 Ion exchange capacity is important to soil fertilityimportant to soil fertility

Soil soluble nutrients are charged particles, Soil soluble nutrients are charged particles, ions. ions.

Cations: positively charged (CaCations: positively charged (Ca2+2+, Mg, Mg2+2+, , NHNH44

++))

Anions: negatively charged (NOAnions: negatively charged (NO33––, PO, PO33

4–4–))

Ions are attached to soil particles, so do Ions are attached to soil particles, so do not leach out of the soil.not leach out of the soil.

Ion exchange capacity: total number of Ion exchange capacity: total number of charged sites on soil particles in a charged sites on soil particles in a standard volume of soil.standard volume of soil.

Soils have an excess of negative Soils have an excess of negative charged sitescharged sites

Cationic exchange Cationic exchange dominant (colloids)dominant (colloids)

Cation exchange Cation exchange capacity (CEC): capacity (CEC): total # of total # of negatively charged sites, located on negatively charged sites, located on the leading edges of clay particles the leading edges of clay particles

and SOM.and SOM. Concentration and Concentration and

affinityaffinity

Al3+ > H+ > Ca2+ > Mg2+ > K+ = NH4+

> Na+

Soils have an excess of negative Soils have an excess of negative charged sitescharged sites

Change in pH affects Change in pH affects binding capacity for binding capacity for ionsions• ImmovableImmovable

Hydrogen (H+)Hydrogen (H+) Aluminum (Al+++)Aluminum (Al+++)

• Removable in orderRemovable in order Calcium (Ca++)Calcium (Ca++) Magnesium (Mg++)Magnesium (Mg++) Potassium (K+)Potassium (K+) Ammonium (NH4+)Ammonium (NH4+) Sodium (Na+)Sodium (Na+)

Process of cation exchange in soilsProcess of cation exchange in soils

In soils with high Mg++ or Ca++, K+ is lacking, why?

Regional differences in geology, Regional differences in geology, climate, and vegetation give rise to climate, and vegetation give rise to characteristically different soilscharacteristically different soils

The broadest level of soil The broadest level of soil classification is classification is soil order soil order

5.7 Basic Soil Formation Processes 5.7 Basic Soil Formation Processes Produce Different SoilsProduce Different Soils

• EntisolEntisol• MollisolMollisol• AlfisolAlfisol• AndisolAndisol• AridisolAridisol• InceptisolInceptisol

• HistosolHistosol• OxisolOxisol• VertisolVertisol• SpodosolSpodosol• UltisolUltisol• GelisolGelisol

There are twelve orders of soil

5.7 Soils vary with climate and vegetation5.7 Soils vary with climate and vegetation

UltisolsUltisols UltisolUltisol

• Warm climate soilWarm climate soil• Redish or yellowishRedish or yellowish• Low nutrient contentLow nutrient content

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

Salinization (Aridisol)Salinization (Aridisol)

Salinization: Salinization: in very dry in very dry climates and when loss of soil climates and when loss of soil moisture due to ET exceeds moisture due to ET exceeds PPT, water leaves the soil PPT, water leaves the soil through the surface. The through the surface. The minerals (NaCl) dissolved minerals (NaCl) dissolved move upward from the move upward from the groundwater and result in a groundwater and result in a salt crust on the surface of salt crust on the surface of the soil. the soil.

Irrigation of dryland can result Irrigation of dryland can result salinization. This becomes a salinization. This becomes a problem in US southwest, problem in US southwest, Australia, Northern Africa, Australia, Northern Africa, China, and major areas of China, and major areas of dryland irrigation.dryland irrigation.

5.8 Light distribution within plant 5.8 Light distribution within plant canopycanopy

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

Plant cover dramatically changes the light Plant cover dramatically changes the light environment underneath itenvironment underneath it

types of plants making up the cover can have an types of plants making up the cover can have an effect (small portion reach ground)effect (small portion reach ground)• Deciduous forest Deciduous forest –– 1% to 5% 1% to 5%• Coniferous forest Coniferous forest –– 10% to 15% 10% to 15%• Tropical rain forest Tropical rain forest –– 0.25% to 2% 0.25% to 2%

Total LAI=315/78.5=4

Effect of leaf angle on Effect of leaf angle on leaf area index and leaf area index and light penetrationlight penetration

Season also Season also affects the light affects the light penetrationpenetration

The ground under The ground under a deciduous forest a deciduous forest will undergo a will undergo a seasonal cycle seasonal cycle affected by leaf affected by leaf lossloss

The ground under The ground under a coniferous forest a coniferous forest will undergo a will undergo a seasonal cycle seasonal cycle unaffected by leaf unaffected by leaf lossloss

The ground under The ground under a tropical a tropical rainforest will rainforest will neither have a neither have a seasonal cycle or seasonal cycle or an effect from leaf an effect from leaf drop drop

The greater the surface area of The greater the surface area of leaves, the less light will penetrate leaves, the less light will penetrate the canopy and reach the groundthe canopy and reach the ground

The attenuation (vertical reduction) The attenuation (vertical reduction) of light through a stand of plants is of light through a stand of plants is estimated using estimated using Beer’s lawBeer’s law

Quantifying Ecology: Beer’s Law Quantifying Ecology: Beer’s Law and the Attenuation of Lightand the Attenuation of Light

Beer’s Law

The EndThe End

Basic Soil Formation Processes Basic Soil Formation Processes Produce Different SoilsProduce Different Soils

Laterization Laterization is a process common to soils is a process common to soils found in humid environments in the found in humid environments in the tropical and subtropical regions tropical and subtropical regions heavy heavy leaching of nutrientsleaching of nutrients

Calcification Calcification occurs when evaporation occurs when evaporation and water uptake by plants exceed and water uptake by plants exceed precipitation precipitation deposition and buildup of deposition and buildup of alkaline salts (CaCOalkaline salts (CaCO33) in the subsoil) in the subsoil

SalinizationSalinization occurs in very dry climates occurs in very dry climates or coastal regions as a result of salt spray or coastal regions as a result of salt spray salt deposits near the soil surface salt deposits near the soil surface

PodzolizationPodzolization occurs in cool, moist occurs in cool, moist climates where coniferous vegetation climates where coniferous vegetation (pine forests) dominates (pine forests) dominates acidic soil acidic soil enhances leaching of cations, iron, and enhances leaching of cations, iron, and aluminum from the topsoilaluminum from the topsoil

GleizationGleization occurs in areas with high occurs in areas with high rainfall or in areas of poor drainage rainfall or in areas of poor drainage organic matter is slowly decomposed and organic matter is slowly decomposed and accumulates in the upper layers of soilaccumulates in the upper layers of soil

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