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Lecture 11 Outline (Ch. 37)

I. Mineral Acquisition

II. Soil Conservation

III. Essential Nutrients

IV. Relationships with other organisms

V. Lecture Concepts

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Overview: A Nutritional Network

• Every organism

– Continually exchanges energy and materials with its environment

• The branching root and shoot system provides high SA:V to collect resources

– Plants’ resources are diffuse (scattered, at low concentration)

What are these diffuse resources?

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Light

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Can a plant grow there?– Climate– Soil Quality

• Texture: type of soil particles• Composition: organic and inorganic components

Mineral Acquisition

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• After heavy rainfall, water drains away from the larger spaces in soil

– But smaller spaces retain water because of its attraction to surfaces of clay and other particles

• The film of loosely bound water– available to plants

(a) Soil water. A plant cannot extract all the water in the soil because some of it is tightly held by hydrophilic soil particles. Water bound less tightly to soil particles can be absorbed by the root.

Soil particle surrounded byfilm of water

Root hair

Water available to plant

Air space

Mineral Acquisition

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• Acids derived from roots contribute to a plant’s uptake of minerals– When H+ displaces mineral cations from clay particles

Figure 37.3

(b) Cation exchange in soil. Hydrogen ions (H+) help make nutrients available by displacing positively charged minerals (cations such as Ca2+) that were bound tightly to the surface of negatively charged soil particles.

H2O + CO2

H2CO3 HCO3– +

Root hair

K+

Cu2+ Ca2+Mg2+

K+

K+

H+

H+

Soil particle–

– – – – – – ––

Mineral Acquisition

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Soil Conservation and Sustainable Agriculture• In contrast to natural ecosystems agriculture depletes

– mineral content of the soil– taxes water reserves– encourages erosion

• The goal of soil conservation strategies: minimize this damage

Fertilizers – what’s the problem?

Commercially produced fertilizers: Minerals are either mined or prepared industrially

Irrigation – Why? Why not?– Can change the chemical makeup of soil

Erosion – Why? Why should we care?• Topsoil from thousands of acres of farmland is …

– lost to water and wind erosion each year in the U.S.

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• Agricultural researchers– Are developing ways to maintain crop yields while

reducing fertilizer and water use.

• Certain precautions– Can prevent the loss of topsoil

Figure 37.5

Soil Conservation and Sustainable Agriculture

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10Essential Nutrients and Deficiencies• Plants require certain chemical elements to complete

their life cycle

• Plants derive most of their organic mass from the CO2 of air

– But they also depend on soil nutrients such as water and minerals

Essential elements:Required for a plant to complete its life cycle

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Essential elements in plants

• Nine of the essential elements are called macronutrients– Because plants require

them in relatively large amounts

• The remaining eight essential elements are known as micronutrients– Because plants need

them in very small amounts

Table 37.1

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Nitrogen, Soil Bacteria and Nitrogen Availability

• Plants compete fiercely for key nutrients like Nitrogen

• Nitrogen is needed for: Proteins, nucleic acids, chlorophyll, etc.

• Nitrogen-fixing soil bacteria convert atmospheric N2

– To nitrogenous minerals that plants can absorb

Figure 37.9

Atmosphere

N2

Soil

N2 N2

Nitrogen-fixingbacteria

Organicmaterial (humus)

NH3

(ammonia)

NH4+

(ammonium)

H+

(From soil)

NO3–

(nitrate)Nitrifyingbacteria

Denitrifyingbacteria

Root

NH4+

Soil

Atmosphere

Nitrate and nitrogenous

organiccompoundsexported in

xylem toshoot system

Ammonifyingbacteria

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Symptoms of Mineral Deficiency

• The symptoms of mineral deficiency depend on – nutrient’s function– nutrient’s mobility within the plant

Figure 37.7

Phosphate-deficient

Healthy

Potassium-deficient

Nitrogen-deficient

• The most common deficienciesAre those of nitrogen, potassium, and phosphorus

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• Root nodulation• Mycorrhizae• Parasitic plants• Carnivorous plants

Relationship with other organisms

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Symbiotic Nitrogen Fixation• Symbiotic relationships between certain nitrogen-fixing

bacteria and certain plants.– Mainly legume family (e.g. peas, beans)

Why is this a symbiosis?

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• Nodules: Swellings of plant cells “infected” by Rhizobium bacteria

Figure 37.10a

(a) Pea plant root

Nodules

Roots

• Inside the nodule– Rhizobium bacteria assume a

form called bacteroids, which are contained within vesicles formed by the root cell

Figure 37.10b(b) Bacteroids in a soybean root

nodule. In this TEM, a cell froma root nodule of soybean is filledwith bacteroids in vesicles. The cells on the left are uninfected.

5 m

Bacteroidswithinvesicle

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• Each legume is associated with a particular strain of Rhizobium

• Nodule development depends on a– chemical dialogue between Rhizobium bacteria and root

cells of their specific plant hosts

Figure 37.11

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Mycorrhizae and Plant Nutrition

• Mycorrhizae

– Symbiotic relationship between a root and fungus

– Most but not all plants.

• The fungus gets: supply of sugars from the plant

• The fungus gives: Increases the surface area for water and mineral absorption

• Agriculturally, farmers and foresters …

– Often inoculate seeds with spores of mycorrhizal to promote mycorrhizal relationships.

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Two Common Types of Mycorrhizae

• In ectomycorrhizae– The mycelium of the fungus forms a

dense sheath over the surface of the root

Figure 37.12a

Mantle(fungal sheath)

Epidermis Cortex Mantle(fungalsheath)

Endodermis

Fungalhyphaebetweencorticalcells (colorized SEM)

100 m

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Two Common Types of Mycorrhizae

• In endomycorrhizae– Fungal hyphae extend into the root

and form arbuscules

Figure 37.12b

Epidermis Cortex

Fungalhyphae

Roothair

10 m

Endodermis

Vesicle

Casparianstrip

Arbuscules

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Epiphytes, Parasitic and Carnivorous Plants

Figure 37.14

Staghorn fern, an epiphyte

EPIPHYTES

PARASITIC PLANTS

CARNIVOROUS PLANTS

Mistletoe, a photosynthetic parasite Dodder, a nonphotosynthetic parasite

Host’s phloem

Haustoria

Indian pipe, a nonphotosynthetic parasite

Venus’ flytrapPitcher plants Sundews

Dodder

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Self-Check

Macronutrients (not a complete list)

Sources; Any special methods for obtaining.

Carbon

Oxygen

Hydrogen

Nitrogen

Phosphorus

Magnesium

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Lecture 11 concepts

- Name the resources that plants need and must acquire.

- Explain how plants uptake minerals via their roots.

- What are the concerns for soil conservation?

- Define macronutrient and micronutrient. List the macronutrients.

- Describe how plants obtain carbon.

- Explain how plants acquire nitrogen (more than one way).

- Define ‘symbiosis’. Discuss the symbioses with bacteria and fungi.

- Describe epiphytes, parasitic, and carnivorous plants.

- Make a list of new vocabulary with definitions.