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Chapter 37
Plant Nutrition
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Overview: A Nutritional Network
• Every organism
– Continually exchanges energy and materials
with its environment
• For a typical plant
– Water and minerals come from the soil, while
carbon dioxide comes from the air
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• The branching root system and shoot system
of a vascular plant
– Ensure extensive networking with both
reservoirs of inorganic nutrients
Figure 37.1
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• Concept 37.1: 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
CO2, the source
of carbon for
Photosynthesis,
diffuses into
leaves from the
air through
stomata.
H2O
CO2
O2
Through
stomata, leaves
expel H2O and
O2.
O2
Minerals
Figure 37.2
Roots absorb
H2O and
minerals from
the soil.
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CO2
H2O
Roots take in
O2 and expel
CO2. The plant
uses O2 for cellular
respiration but is
a net O2 producer.
Macronutrients and Micronutrients
• More than 50 chemical elements
– Have been identified among the inorganic
substances in plants, but not all of these are
essential
• A chemical element is considered essential
– If it is required for a plant to complete a life
cycle
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• Researchers use hydroponic culture
– To determine which chemicals elements are
essential
APPLICATION
In hydroponic culture, plants are grown in mineral solutions without soil. One use of hydroponic
culture is to identify essential elements in plants.
TECHNIQUE
Plant roots are bathed in aerated solutions of known mineral composition. Aerating the water provides
the roots with oxygen for cellular respiration. A particular mineral, such as potassium, can be omitted to test whether it is
essential.
Control: Solution
containing all minerals
Figure 37.3
Experimental: Solution
without potassium
RESULTS
If the omitted mineral is essential, mineral deficiency symptoms occur, such as stunted growth and
discolored leaves. Deficiencies of different elements may have different symptoms, which can aid in diagnosing mineral
deficiencies in soil.
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• Essential elements in plants
Table 37.1
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• 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
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Symptoms of Mineral Deficiency
• The symptoms of mineral deficiency
– Depend partly on the nutrient’s function
– Depend on the mobility of a nutrient within the
plant
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• Deficiency of a mobile nutrient
– Usually affects older organs more than young
ones
• Deficiency of a less mobile nutrient
– Usually affects younger organs more than
older ones
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• The most common deficiencies
– Are those of nitrogen, potassium, and
phosphorus
Healthy
Phosphate-deficient
Potassium-deficient
Nitrogen-deficient
Figure 37.4
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• Concept 37.2: Soil quality is a major determinant
of plant distribution and growth
• Along with climate
– The major factors determining whether particular
plants can grow well in a certain location are the
texture and composition of the soil
• Texture
– Is the soil’s general structure
• Composition
– Refers to the soil’s organic and inorganic chemical
components
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Texture and Composition of Soils
• Various sizes of particles derived from the
breakdown of rock are found in soil
– Along with organic material (humus) in various
stages of decomposition
• The eventual result of this activity is topsoil
– A mixture of particles of rock and organic
material
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• The topsoil and other distinct soil layers, or
horizons
– Are often visible in vertical profile where there is a
road cut or deep hole
The A horizon is the topsoil, a mixture of
broken-down rock of various textures, living
organisms, and decaying organic matter.
A
B
The B horizon contains much less organic
matter than the A horizon and is less
weathered.
C
The C horizon, composed mainly of partially
broken-down rock, serves as the “parent”
material for the upper layers of soil.
Figure 37.5
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• After a heavy rainfall, water drains away from the
larger spaces of soil
– But smaller spaces retain water because of its
attraction to surfaces of clay and other particles
• The film of loosely bound water
– Is usually available to plants
Soil particle surrounded by
film of water
Root hair
Water available
to plant
Air space
Figure 37.6a
(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.
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• Acids derived from roots contribute to a plant’s
uptake of minerals
– When H+ displaces mineral cations from clay
particles
Soil particle
K+
–
–
Cu2+
–
–
K+
–
–
–
Mg2+
– +
K
–
Ca2+
H+
H2O + CO2
H2CO3
HCO3– + H+
Root hair
Figure 37.6b
(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. Plants contribute H+ by secreting it from root hairs
and also by cellular respiration, which releases CO2 into the soil
solution, where it reacts with H2O to form carbonic acid (H2CO3).
Dissociation of this acid adds H+ to the soil solution.
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Soil Conservation and Sustainable Agriculture
• In contrast to natural ecosystems
– Agriculture depletes the mineral content of the
soil, taxes water reserves, and encourages
erosion
• The goal of soil conservation strategies
– Is to minimize this damage
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Fertilizers
• Commercially produced fertilizers
– Contain minerals that are either mined or
prepared by industrial processes
• “Organic” fertilizers
– Are composed of manure, fishmeal, or
compost
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• Agricultural researchers
– Are developing ways to maintain crop yields while
reducing fertilizer use
• Genetically engineered “smart” plants
– Inform the grower when a nutrient deficiency is
imminent
No phosphorus deficiency
Figure 37.7
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Beginning phosphorus
deficiency
Well-developed phosphorus
deficiency
Irrigation
• Irrigation, which is a huge drain on water
resources when used for farming in arid
regions
– Can change the chemical makeup of soil
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Erosion
• Topsoil from thousands of acres of farmland
– Is lost to water and wind erosion each year in
the United States
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• Certain precautions
– Can prevent the loss of topsoil
Figure 37.8
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• The goal of soil management
– Is sustainable agriculture, a commitment
embracing a variety of farming methods that
are conservation-minded
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Soil Reclamation
• Some areas are unfit for agriculture
– Because of contamination of soil or
groundwater with toxic pollutants
• A new method known as phytoremediation
– Is a biological, nondestructive technology that
seeks to reclaim contaminated areas
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• Concept 37.3: Nitrogen is often the mineral that
has the greatest effect on plant growth
• Plants require nitrogen as a component of
– Proteins, nucleic acids, chlorophyll, and other
important organic molecules
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Soil Bacteria and Nitrogen Availability
• Nitrogen-fixing bacteria convert atmospheric N2
– To nitrogenous minerals that plants can absorb as
a nitrogen source for organic synthesis
Atmosphere
N2
N2
Atmosphere
Soil
N2
Nitrogen-fixing
bacteria
Denitrifying
bacteria
H+
Nitrate and
nitrogenous
organic
compounds
exported in
xylem to
shoot system
(From soil)
Soil
+
NH4
NH3
(ammonia)
–
+
NH4
(ammonium)
Nitrifying
bacteria
NO3
(nitrate)
Ammonifying
bacteria
Organic
material (humus)
Figure 37.9
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Root
Improving the Protein Yield of Crops
• Agriculture research in plant breeding
– Has resulted in new varieties of maize, wheat,
and rice that are enriched in protein
• Such research
– Addresses the most widespread form of
human malnutrition: protein deficiency
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• Concept 37.4: Plant nutritional adaptations
often involve relationships with other organisms
• Two types of relationships plants have with
other organisms are mutualistic
– Symbiotic nitrogen fixation
– Mycorrhizae
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The Role of Bacteria in Symbiotic Nitrogen Fixation
• Symbiotic relationships with nitrogen-fixing
bacteria
– Provide some plant species with a built-in
source of fixed nitrogen
• From an agricultural standpoint
– The most important and efficient symbioses
between plants and nitrogen-fixing bacteria
occur in the legume family (peas, beans, and
other similar plants)
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• Along a legumes possessive roots are swellings
called nodules
– Composed of plant cells that have been “infected”
by nitrogen-fixing Rhizobium bacteria
Nodules
Roots
Figure 37.10a
(a) Pea plant root. The bumps on
this pea plant root are nodules
containing Rhizobium bacteria.
The bacteria fix nitrogen and
obtain photosynthetic products
supplied by the plant.
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• Inside the nodule
– Rhizobium bacteria assume a form called
bacteroids, which are contained within vesicles
5 m
formed by the root cell
Bacteroids
within
vesicle
Figure 37.10b
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(b) Bacteroids in a soybean root
nodule. In this TEM, a cell from
a root nodule of soybean is filled
with bacteroids in vesicles. The
cells on the left are uninfected.
• The bacteria of a nodule
– Obtain sugar from the plant and supply the
plant with fixed nitrogen
• Each legume
– Is associated with a particular strain of
Rhizobium
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• Development of a soybean root nodule
1 Roots emit chemical
signals that attract
Rhizobium bacteria.
The bacteria then emit
signals that stimulate
root hairs to elongate
and to form an
infection thread by an
invagination of the
plasma membrane.
Infection
thread
Rhizobium
bacteria
Dividing cells
in root cortex
Bacteroid
Infected
root hair
Dividing cells in
pericycle
1
2
2 The bacteria penetrate
the cortex within the
Infection thread. Cells of
the cortex and pericycle
begin dividing, and
vesicles containing the
bacteria bud into cortical
cells from the branching
infection thread. This
process results in the
formation of bacteroids.
Developing
root nodule
3
3 Growth continues in the
affected regions of the
cortex and pericycle,
and these two masses
of dividing cells fuse,
forming the nodule.
4
4 The nodule develops
vascular tissue that
supplies nutrients to the
nodule and carries
nitrogenous compounds
into the vascular
cylinder for distribution
throughout the plant.
Bacteroid
Figure 37.11
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Bacteroid
Nodule
vascular
tissue
The Molecular Biology of Root Nodule Formation
• The development of a nitrogen-fixing root
nodule
– Depends on chemical dialogue between
Rhizobium bacteria and root cells of their
specific plant hosts
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Symbiotic Nitrogen Fixation and Agriculture
• The agriculture benefits of symbiotic nitrogen
fixation
– Underlie crop rotation
• In this practice
– A non-legume such as maize is planted one
year, and the following year a legume is
planted to restore the concentration of nitrogen
in the soil
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Mycorrhizae and Plant Nutrition
• Mycorrhizae
– Are modified roots consisting of mutualistic
associations of fungi and roots
• The fungus
– Benefits from a steady supply of sugar donated by
the host plant
• In return, the fungus
– Increases the surface area of water uptake and
mineral absorption and supplies water and
minerals to the host plant
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The Two Main Types of Mycorrhizae
• In ectomycorrhizae
– The mycelium of the fungus forms a dense sheath
over the surface of the root
Epidermis
a Ectomycorrhizae. The mantle
(a)
of the fungal mycelium
ensheathes the root. Fungal
hyphae extend from the mantle
into the soil, absorbing water
and minerals, especially
phosphate. Hyphae also
extend into the extracellular
spaces of the root cortex,
providing extensive surface
area for nutrient exchange
between the fungus and its
host plant.
Cortex
Mantle
(fungal
sheath)
100 m
Endodermis
Mantle
(fungal sheath)
Figure 37.12a
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Fungal
hyphae
between
cortical
cells
(colorized SEM)
• In endomycorrhizae
– Microscopic fungal hyphae extend into the root
(b)
2 Endomycorrhizae. No mantle
forms around the root, but
microscopic fungal hyphae
extend into the root. Within
the root cortex, the fungus
makes extensive contact with
the plant through branching of
hyphae that form arbuscules,
providing an enormous
surface area for nutrient
swapping. The hyphae
penetrate the cell walls, but
not the plasma membranes,
of cells within the cortex.
Epidermis
Cortex
Cortical cells
10 m
Endodermis
Fungal
hyphae
Vesicle
Casparian
strip
Root
hair
Arbuscules
(LM, stained specimen)
Figure 37.12b
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Agricultural Importance of Mycorrhizae
• Farmers and foresters
– Often inoculate seeds with spores of
mycorrhizal fungi to promote the formation of
mycorrhizae
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Epiphytes, Parasitic Plants, and Carnivorous Plants
• Some plants
– Have nutritional adaptations that use other
organisms in nonmutualistic ways
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• Exploring unusual nutritional adaptations in plants
EPIPHYTES
Staghorn fern, an epiphyte
PARASITIC PLANTS
Host’s phloem
Dodder
Haustoria
Mistletoe, a photosynthetic parasite
Dodder, a nonphotosynthetic
parasite
Indian pipe, a nonphotosynthetic parasite
CARNIVOROUS PLANTS
Figure 37.13
Venus’ flytrap
Pitcher plants
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Sundews