1. Biology, 9th ed, Sylvia Mader
Chapter 26
Plant Nutrition
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Leaf
intercellular
spaces
xylem
phloem
stoma O2
CO2
H2O O2
CO2
H2O
sugar
H2O
Stem
CO2 O2
H2O
xylem
phloem
H2O
sugar
Root
H2O O2
H2O
CO2
minerals
xylem
phloem

2. Outline Essential Inorganic Nutrients Water & Mineral Uptake
Soil Formation
Soil Profiles
Soil Erosion
Water & Mineral Uptake
Transport Mechanisms
Water and Minerals
Organic Nutrients

3. Plant Nutrition and Soil
Essential Inorganic Nutrients
About 95% of a plant’s dry weight is carbon, hydrogen, and oxygen
Primary nutrients are carbon dioxide and water
A nutrient is essential if
It has an identifiable role,
Another nutrient cannot substitute for it, and
A deficiency of the nutrient causes a plant to die
Macronutrients
Micronutrients

4. Overview of Plant Nutrition
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. O2
CO2
H2O O2
H2O
CO2
minerals

5. Nutrient Deficiencies
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
a. Solution lacks nitrogen
Complete nutrient solution
b. Solution lacks phosphorus
Complete nutrient solution
c. Solution lacks calcium
Courtesy Mary E. Doohan
Complete nutrient solution

6. Soil Formation Soil formation begins with weathering of rock
Organisms also play an important role
Lichens and Mosses
Humus begins to accumulate
Under ideal conditions, a centimeter of soil may develop within 15 years

7. Nutritional Function of Soil
Soil is a mixture of:
Mineral particles
Decaying organic material
Living organisms
Air, and
Water
Roots take up oxygen from air spaces
Soils are a mixture of three types of particles
Sand
Clay
Silt

8. Absorbing Minerals
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
negatively charged soil particle K+ K+ K+
Ca2+
Ca2+
root hair
Ca2+ K+ H+ H+
Ca2+ K+
Ca2+ K+
film of water
air space
epidermis of root

9. Soil Profiles
A soil profile is a vertical section from ground surface to unaltered rock below
Parallel layers - Horizons
A (topsoil) - Litter and humus
B (subsoil) - Inorganic nutrients
C (parent material) - Weathered rock
Because parent material and climate differ, the soil profile varies according to the particular ecosystem

10. Simplified Soil Profile
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Soil horizons
Topsoil: humus
plus living
organisms A
Zone of leaching:
removal of nutrients B
Subsoil:
accumulation
of minerals and
organic materials
Parent material:
weathered rock C

11. Soil Erosion
Soil erosion occurs when water or wind carry soil away to a new location
Worldwide, erosion removes about 25 billion tons of topsoil annually
Deforestation
Desertification
Poor farming practice

12. Water and Mineral Uptake
Water and minerals enter the roots of flowering plants through the same pathways
Between porous cell walls, then forced into endodermal cells by the Casparian strip
Through root hairs, through cells across the cortex and endodermis via cytoplasmic strands within plasmodesmata
Water enters root cells when their osmotic pressure is lower than that of the soil
Minerals are actively taken up by plant cells and are transported in the xylem along with water 12

13. Water and Mineral Uptake
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
endodermis
pericycle
phloem
xylem
cortex
50 mm
An ATP-driven
pump transports
H+ out of cell.
The electrochemical
gradient causes K+
to enter by way of a
channel protein.
Endodermal Cell 1 2
vascular cylinder H+ I- I-
pericycle K+ K+ H+
ATP P I- I- H+
ADP +
endodermis
and Casparian
strip K+ H+ K+ K+ I-
cortex H+ I- H+ K+
epidermis
Pathway A
of water and
minerals H+ H+ 3
Negatively charged ions
(I−) are transported
along with H+ into cell.
pathway B
of water and
minerals
Water Outside Endodermal Cell a.
root hair b.
a: © CABISCO/Phototake

14. Adaptations of Roots for Mineral Uptake
Important Symbiotic Relationships
Rhizobium bacteria live in root nodules
Bacteria fix atmospheric nitrogen
Host plant provides the bacteria with carbohydrates
Mycorrhizal association between fungi and plant roots
Fungus increases the surface area for water and mineral uptake and break down organic matter
Root provides the fungus with sugars and amino acids
Parasitic plants
Carnivorous plants

15. Root Nodules root nodule bacteria Portion of infected cell
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
root
nodule
bacteria
Portion of infected cell
(Top): © Dwight Kuhn; (Circle): © E.H. Newcomb & S.R. Tardon/Biological Photo Service

16. Mycorrhizae Mycorrhizae present Mycorrhizae not present mycorrhizae
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Mycorrhizae present
Mycorrhizae not present
mycorrhizae
(Top): © B. Runk/S. Schoenberger/Grant Heilman Photography; (Circle): © Dana Richter/Visuals Unlimited

17. Other Ways to Acquire Nutrition
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
dodder
(brown)
bulbs release
digestive enzymes
a. Dodder, Cuscuta sp.
Sundew leaf
enfolds prey
sticky
hairs
narrow
leaf form
b. Cape sundew , Drosera capensis
a: © Kevin Schafer/Corbis; b(Plant): © Barry Rice/Visuals Unlimited; b(Leaf): © Dr. Jeremy Burgess/Photo Researchers, Inc.

18. Transport Mechanisms in Plants
Vascular tissues transport water and nutrients
Xylem transports water and minerals
Two types of conducting cells
Tracheids
Vessel Elements
Water flows passively from an area of higher water potential to an area of lower water potential
Phloem transports organic materials
Conducting cells are sieve-tube members
Have companion cells to provide proteins
End walls are sieve plates
Plasmodesmata extend through sieve plates

19. Plant Transport System
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Leaf
intercellular
spaces
xylem
phloem
stoma O2
CO2
H2O O2
CO2
H2O
sugar
H2O
Stem
xylem
phloem
sugar
Root
H2O
H2O
xylem
phloem

20. The Concept of Water Potential
Potential energy is stored energy
Water potential is the energy of water.
Water moves from a region of higher potential to a region of lower potential
In terms of cells, two factors usually determine water potential:
Water pressure across a membrane
Solute concentration across a membrane

21. The Concept of Water Potential
Pressure potential is the effect that pressure has on water potential.
Water moves across a membrane from the area of higher pressure to the area of lower pressure.
The higher the water pressure, the higher the water potential.
Osmotic potential takes into accounts the presence of solutes
Water tends to move from the area of lower solute concentration to the area of higher solute concentration.
The lower the concentration of solutes (osmotic potential), the higher the water potential.

22. Water Potential and Turgor Pressure
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
central vacuole
Wilted
central vacuole
Turgid
cell wall
cell wall
H2O
enters
the cell
Extracellular fluid:
Equal water
potential inside and
outside the cell
water potential
pressure potential
osmotic potential
higher
Inside the cell:
Pressure potential
increases until
the cell is turgid
water potential
pressure potential
osmotic potential
lower
a. Plant cells need water.
b. Plant cells are turgid.
(Both): © Dwight Kuhn

23. Water Transport Xylem vessels form an open pipeline
The vessel elements are separated by perforated plates
Water moves into an out of tracheids through pits
Water entering roots creates a positive pressure (root pressure)
Pushes xylem sap upward
May be responsible for guttation
Water forced out vein endings along edges of leaves

24. Conducting Cells of Xylem
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
pits
20 mm
20 mm
50 mm
a. Perforation plate with a single, large opening
b. Perforation plate with a series of openings
c. Tracheids
a, b: Courtesy Wilfred A. Cote, from H.A. Core, W.A. Cote, and A.C. Day, Wood: Structure and Identification 2/e; c: Courtesy W.A. Cote, Jr., N.C. Brown Center for Ultrastructure Studies, SUNY-ESF

25. © Ed Reschke/Peter Arnold, Inc.
Guttation
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
© Ed Reschke/Peter Arnold, Inc.

26. Cohesion-Tension Model
Cohesion-tension model of xylem transport suggests a passive xylem transport
Cohesion is the tendency of water molecules to cling together
Adhesion is the ability of the polar water molecules to interact with molecules of vessel walls
A continuous water column moves passively upward due to transpiration

27. Cohesion-Tension Model
Leaves
Transpiration causes water loss through stomata
Water molecules that evaporate are replaced by water molecules from leaf veins
Due to cohesion, transpiration exerts a pulling force (tension) drawing water through the xylem to the leaf cells
Waxy cuticle prevents water loss when stomata are closed
Stem
Tension in xylem pulls the water column upward
Roots
Water enters xylem passively by osmosis and is pulled upward due to tension in xylem 27

28. Cohesion-Tension Model of Xylem Transport
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
mesophyll
cells
xylem in
leaf vein
Leaves
creates tension.
• Transpiration
stoma
• Tension pulls the water
column upward from
the roots to the leaves.
intercellular
space
H2O
cohesion by hydrogen bonding
between water molecules
adhesion due to
polarity of water
molecules
H2O
cell wall
water molecule
Stem
• Cohesion makes
water continuous.
• Adhesion keeps water
column in place.
xylem
H2O
water molecule
root hair
H2O
Roots
• Water enters xylem at
root.
from leaves to the root.
• Water column extends
xylem

29. Opening and Closing of Stomata
Each stoma in leaf epidermis is bordered by guard cells
Increased turgor pressure in guard cells opens stoma
Active transport of K+ into guard cells causes water to enter by osmosis and stomata to open
Opening and closing of stomata is regulated by light

30. Opening and Closing of Stomata
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Open stoma
H2O
H2O
Vacuole K+
stoma
25 m
25 m
K+ enters guard cells, and water follows. a.
25 mm
Closedstoma
H2O
H2O K+
K+ exits guard cells, and water follows. b.
25 mm

31. Organic Nutrient Transport
Role of Phloem
Phloem transports sugar
Girdling of tree below the level of leaves causes bark to swell just above the cut
Sugar accumulates in the swollen tissue
Radioactive tracer studies confirm that phloem transports organic nutrients
Phloem sap can be collected using aphids

32. Acquiring Phloem Sap a. An aphid feeding on a plant stem
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
a. An aphid feeding on a plant stem
b. Aphid stylet in place
a: © M.H. Zimmermann, Courtesy Dr. P.B. Tomlinson, Harvard University; b: © Steven P. Lynch

33. Pressure-Flow Model of Phloem Transport
Sieve tubes form a continuous pathway for organic nutrient transport
Sieve-tube members are aligned end to end
Strands of plasmodesmata extend through sieve plates between sieve-tube members
Positive pressure drives the movement of sap in sieve tubes
Sucrose is actively transported into phloem at the leaves
Water follows by osmosis, creating positive pressure
The increase in pressure causes flow that moves water and sucrose to a sink

34. Pressure-flow Model of Phloem Transport
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
mesophyll cell of leaf
Leaf
phloem
xylem
sugar
water
xylem
phloem
cortex cell
of root
xylem
phloem
Root

35. Review Essential Inorganic Nutrients Water & Mineral Uptake
Soil Formation
Soil Profiles
Soil Erosion
Water & Mineral Uptake
Transport Mechanisms
Water and Minerals
Organic Nutrients

36. Biology, 9th ed, Sylvia Mader
Chapter 26
Plant Nutrition