biol 100c soil & mineral nutrients

8/4/2019 BIOL 100C Soil & Mineral Nutrients

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Soils & Mineral Nutrients


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Soil Components

Inorganicderived from weathered rockWeathering

the forces applied by rain, running

water, and windbegins the process of building soilfrom solid rock.

Organicresidue of partially decayed organisms

Watercontains mineral ions and dissolved gases

Airatmospheric gasesdissolved in water


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Soil Formation Begins withErosion of Rock

Soil texture is categorized by particlesize: Gravel Sand

Silt Clay

(>2.0 mm) (0.022.0 mm)

(0.0020.02 mm) (


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SandClay

Silt


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A mixture of sand, silt, and clay in equalproportions is a loam soil. If one componentoccurs in a higher proportion than the others a

sandy loam, silt loam, or clay loam results

The organic component of soil is humus

Topsoil is a mixture of elements from inorganicand organic sources

Texturethe proportions of different-sizedparticles present in soilaffects the ability ofroots to penetrate the soil and the ability of thesoil to hold water.


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Mature Soils Are a Complex Mixture ofOrganic and Inorganic Components

Earthworm

Plants

Ant

Humus

120 Beetle grub

Humus containsa high density ofdiverse organisms,dead and alive

Bacteria andarchaea

Protists

Nematode

Fungus

Soildepth

(cm)

75

25

50


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RBedrockunaltered material

General Soil Profile


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B

Various


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Soil Water Gravitationalwaterportion of water added to soil

that mostly moves rapidly down past root levelbecause of the pull of gravitydeepest unavailable toplants

Capillarywaterportion of water that forms shells

around soil particles

mostly at root level

availableto plants Hygroscopicwaterportion of water that is so tightly

bound to soil particles that roots cannot absorb itunavailable to plants

Fieldcapacitytotal amount of capillary waternearsaturation pointafter the movement of gravitationalwater has ceased

Permanent wiltingpointthe point at which a plant

wilts, and will not recover


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Deepest unavailablebeyond root level


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Soil Characteristics Porositythe size of spaces between soil

particles that affects the movement of waterdown through the soil

Water holdingcapacitysoil water retention

Acidity and Alkalinity

Fertility

soil mineral content and availability

Path of water

through poresbetween soilparticles


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(low porosity)

(high porosity)


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Water Holding Capacity As related to soil particle

sizeinversely proportionalto porosity

Clay and humus particlesare negatively charged, andattract water molecules

Clay particles are laminatedwith large surface area


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Acidity & Alkalinity

Affects absorption of some minerals

Most plants prefer a neutral to slightlyacidic soil

Soil pH can be adjusted:

To increase acidityadd sulfur or humus

To increase alkalinity

add calciumcarbonate (limestone)


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Nutrient Availability as influenced by soil acidity or alkalinity


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Soil Fertility Cation Exchange occurs when protons or other cations in soil

water bind to negative charges on soil particles, and cause

bound cations such as magnesium or calcium to be released,making them available to nearby plant roots.

1) cations (positively charged ions) are attracted to negatively

charged clay particles, and held at their surfaces2) plant roots secrete H+ that combines with CO2 in the soilsolution to form carbonic acid

3) carbonic acid breaks down releasing H+ and bicarbonateions

4) H+ replaces cations on clay particles, and cations arereleased for absorption by roots

Cation exchange by humus particles--humus may also undergosome cation exchange because of negatively charged

component particles


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Cations Tend to Bind to Soil Particles; Anions Stay in Solution

Sand grain

Anions usually dissolve in soil water, theyarereadily available for absorption by root hairs

Cations often interact withnegativecharges on the surface of clay

Clay particle

Clay particle

Clay particle

Root hair

Sand grain

Clay particle

Organic matterOrganic

matter


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CationExchange

CO2

CO2+H2OH2CO3HCO3- + H+


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Cation Exchange Releases Nutrients

Bound to Soil Particles

Cation exchange releases nutrients

Clay or organic matter

Root hair

Protons in soil waterReleasednutrients

which are absorbed by roots or leached in heavy rains.

Uptake

Cation exchange helps prevents mineralleachingloss ofmineral nutrients common in highly porous soils such asthose of rainforestsby holding minerals at the surface ofclay particles, and deterring their removal from root level bygravitational water flow.

Figure 38 8 Table 38 2


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Figure 38-8-Table 38-2


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Mineral Nutrients EssentialNutrientsminerals requiredfor growth, maintenance, and

reproduction is an element that is required for both normal growth and

reproduction and for a specific structure or metabolic function. There are17 essential nutrients for most vascular plants. Essential nutrientsavailable from H2O or CO2 are oxygen (O), carbon (C), and hydrogen (H).They make up 96% of the plant.

Essential nutrients available from soil can be divided into macronutrients

and micronutrients.

Macronutrientsminerals required by plants in large quantitiesThey arenitrogen (N), potassium (K), calcium (Ca), magnesium (Mg), phosphorus(P), and sulfur (S).

Limiting nutrients are macronutrients that commonly act as limits onplant growth. N, P, and K are often limiting nutrients.

Micronutrientsminerals required by plants in trace amountsExamplesinclude iron, zinc, boron, copper, and nickel.

Figure 38-1-Table 38-1-1


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Figure 38 1 Table 38 1 1

Figure 38-1-Table 38-1-2


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Figure 38 1 Table 38 1 2

Chlorophyll component

. Stomata function


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Symptoms of Deficiencies in Macronutrients

Nitrogen (N)chlorosis,uniform color loss; yellowing of

leaves Phosphorous(P)stunted

growth; dark leaves(sometimes purplish); curlingof leaves

Potassium (K)

yellowing ofleaves at margins; mottled

leaves Calcium (Ca)death of

growing points; yellowing and

brown spots on leaves;withered leaf tips Magnesium (Mg)leaves

yellow between veins; deadspots on leaves

Sulfur (S)

leaf veins yellow;pale leaves with dead spots


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Fertilizers are nutrient

supplements. Mostgeneral fertilizerscontain only nitrogen,phosphorous, andpotassium. Other

macronutrients andmicronutrients can besupplied by specializedplant foods

NPK ratioindicatesrelative proportions ofthese elements


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Symbiotic Associations Enhance


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Symbiotic Associations Enhance

Plant Nutrition

RootNodules

associations of Rhizobiumbacteria with roots; bacteria conduct nitrogenfixation (conversion of elemental nitrogen to NH4

+);plants obtain additional nitrogen supplies; bacteria

obtain shelter and photosynthetic products Mycorrhizaefungal / root associations; increases

surface area of root for water and mineralabsorption; fungus obtains photosynthetic products

1) ectomycorrhizaefungal hyphae do notpenetrate root cellsform dense mantle over root

2) arbuscularmycorrhizaefungal hyphae

penetrate root cell walls

Figure 38-14


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g

Nodule in cross section

Nodules

Roots ofpea plant

Figure 38-15Root


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INFECTION BY NITROGEN-FIXING BACTERIA

Root

Root hair

Cortex cells

Root hair

Rhizobia

Infectionthread

Nodule

Uninfected cell

Rhizobia inside vesicles,inside infected cell

5. Nodule forms from

rapidly dividing cortexcells.

4. Infection thread bursts,releasing rhizobia insidecortex cells.

3. Infection thread growsinto the cortex of the root.

1. Root hairs release aflavonoid that attractsRhizobia. Rhizobiamoveinto hairs.

2.Rhizobiaproliferate insideroot hair and cause aninfection thread to form.


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Arbuscular mycorrhizae

Parasitic Plants achlorophyllous invade stem or root tissues of host


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ParasiticPlantsachlorophyllousinvade stem or root tissues of hostplant

Dodder

Mistletoefacultativeparasite

Snow Plant Indian Pipe

Mistletoe haustoria penetrate hostxylem and extract water and ions


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Insectivorous Plants

Produce enzymes capable of digestinganimal protein

Adaptation to decreased nitrogen

availability in natural habitat (bogs,marshes)

Active trappossess trigger mechanisms

to cause rapid closing of trap Passive trapstationary trap designed to

prevent escape


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Bog

Sundew Venus Fly Trap


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Utricularia

y p

Pitcher plant

Figure 38-17


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Epiphytes grow on trees.

Epiphytes

Water-holding tanks formed by leaves ofan epiphytic bromeliad

Tanks

Epiphytes are plants that are adapted to grow in the absence of soil. They often grow onleaves or branches of trees.

They absorb most of the water and nutrients they need from rainwater, dust, and particles thatcollect in their tissues or in the crevices of bark.

biol 100c soil & mineral nutrients

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