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Chapter 37
• Plant nutrition
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The root system and shoot system
– Ensure networking with both reservoirs of
inorganic nutrients
Figure 37.1
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• Plants require certain chemical elements to
complete their life cycle
• Plants derive organic mass f/ CO2
– Also depend on soil nutrients e.g. water and
minerals
H2O
CO2
CO2, the source
of carbon for
Photosynthesis,
diffuses into
leaves from the
air through
stomata.
O2
Through
stomata, leaves
expel H2O and
O2.
Roots take in
O2 and expel
CO2. The plant
uses O2 for cellular
respiration but is
a net O2 producer.
O2
Minerals
Figure 37.2
Roots absorb
H2O and
minerals from
the soil.
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CO2
H2O
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Macronutrients and Micronutrients
• More than 50 elements identified in plants, but
not all are essential
• Essential element is required for a plant to
complete life cycle
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Hydroponic culture
– Determines 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.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Essential elements in plants
Table 37.1
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 9 essential elements are macronutrients (e.g.
C,H,O,P,N,K)
– Large amounts required
• 8 are micronutrients (e.g.Fe)
– Small amts. required
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Common deficiencies
Healthy
Phosphate-deficient
Potassium-deficient
Nitrogen-deficient
ure 37.4
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• Soil
• Soil + climate
– Major factors determining whether particular
plants can grow well in a certain location
• Texture
– Soil’s general structure
• Composition
– Organic and inorganic chemical components
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Particles derived from the breakdown of rock
found in soil
– Also organic material (humus)
• Result is topsoil
–
A mixture of particles of rock and organic
material
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Topsoil + other distinct soil layers, or horizons
A horizon
The
is the topsoil, a mixture of
broken-down rock of various textures, living
organisms, and decaying organic matter.
A
B
C
B horizon
The
contains much less organic
matter than the A horizon and is less
weathered.
C horizon
The
, 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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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.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Soil Conservation and Sustainable Agriculture
• In contrast to natural ecosystems
– Agriculture depletes the mineral content of
soil, taxes water reserves, and encourages
erosion
• Goal of soil conservation strategies
Minimize damage
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Fertilizers
• Commercially produced fertilizers (N P K)
– Minerals that are either mined or prepared by
industrial processes
• “Organic” fertilizers
– e.g. manure, fishmeal, or compost
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• Agricultural research
– Maintain crop yields while reducing fertilizer use
• Genetically engineered “smart” plants
– Inform the grower of nutrient deficiency
No phosphorus deficiency
Figure 37.7
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Beginning phosphorus
deficiency
Well-developed phosphorus
deficiency
Irrigation
• Huge drain on water resources in arid regions
– Can change the chemical makeup of soil
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Erosion
• Topsoil from thousands of acres of farmland
– Lost to water and wind erosion each year
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• Prevention of topsoil loss
Figure 37.8
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• Goal of soil management
– Sustainable agriculture, a variety of farming
methods that are conservation-minded, e.g.
No-till farming
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• Nitrogen often has the greatest effect on plant
growth
• Plants require nitrogen f/:
– Proteins, nucleic acids, chlorophyll, others
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Soil Bacteria
• Nitrogen-fixing bacteria convert atmospheric N2
to form of N that plants can use
Atmosphere
N2
N2
Atmosphere
Soil
N2
Nitrogen-fixing
bacteria
Denitrifying
bacteria
H+
(From soil)
Soil
+
NH4
NH3
(ammonia)
–
+
NH4
(ammonium)
Organic
material (humus)
Nitrate and
nitrogenous
organic
compounds
exported in
xylem to
shoot system
Nitrifying
bacteria
NO3
(nitrate)
Ammonifying
bacteria
Figure 37.9
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Root
• Two types of relationships plants have with
other organisms are mutualistic
– Symbiotic nitrogen fixation (Rhizobium)
– Mycorrhizae
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Symbiotic N2 Fixation
• Provide plant w/ a built-in source of fixed N2
• Legume family (e.g. peas, beans)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Root nodules
– Composed of plant cells that have been “infected”
by nitrogen-fixing Rhizobium bacteria
Nodules
Roots
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• 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
• Crop rotation
•  Non-legume (e.g corn) planted
one year, following year legume
is planted
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Mycorrhizae
• Mycorrhizae
– Mutualistic associations of fungi and roots
• Fungus steady supply of sugar f/ plant
• In return, the fungus increases the surface area of
water uptake
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Mycorrhizae
Epidermis
(a)
a Ectomycorrhizae. The mantle
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)
Fungal
hyphae
between
cortical
cells
(colorized SEM)
Figure 37.12a
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Mycorrhizae
Epidermis
(b)
Cortex
Cortical cells
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.
10 m
Endodermis
Fungal
hyphae
Vesicle
Casparian
strip
Root
hair
Arbuscules
(LM, stained specimen)
Figure 37.12b
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Epiphytes, Parasitic Plants, and Carnivorous Plants
• Nutritional adaptations that use other
organisms in nonmutualistic ways
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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