Transcript Draft copy - University of California, Davis

Plant Nutrition
Where do Plants get their nutrients?
PLANT: A SUGAR FACTORY
NUTRIENTS AVAILABILITY AND SOIL
The relative
availability of
nutrients to
plant roots
depends on
the pH level
of
the soil.
Plant Nutrients Content in % Compared to Nitrogen
Average Composition of Plant
VISUAL SYMPTOMS ON LEAVES
When inspecting plants for symptoms of nutrient disorders, compare
plants displaying symptoms with normal ones and examine new and
older leaves.
OLDEST LEAVES: nutrient deficiencies generally appear first in the oldest
leaves when nitrogen, phosphorus, potassium, and magnesium are
limiting. These nutrients move from one part of the plant to another as
needed.
YOUNGER LEAVES AND TERMINAL BUDS: show a deficiency when
sulfur, iron, calcium, zinc copper, boron, manganese or chlorine are
limiting. These nutrients do not readily move about in the plant.
Nutrients Deficiency Symptoms on Leaves
The most common symptoms of nutrient deficiency are stunted growth and leaf discoloration.
The position of the symptoms (distal, basal or intermediate) depends on the mobility of the
nutrient inside the plant (young leaves competing with oldest leaves)
Mobile Nutrients - Identification Key
Immobile Nutrients – Identification Key
Limiting Nutrient Theory
Fertilizer Needs related to Soil Content
Organic Fertilizers – Macronutrients Content
Analysis of Organic Fertilizers
Manure
%N
%P
%K
Cow
2,0
2.3
2,4
Horse
1.7
0.7
1,8
Sheep
4,0
1.4
3,5
Poultry
4,0
4,0
2,0
How Plant reacts to Fertilizers
Nutrients Removal: Apple
N (KG)
P (KG)
K (KG)
Mg (Ca)
Ca (KG)
Nutrient
removed per
ton apple
0.5
0.1
1.1
0.05
0.05
Nutrient
removal at 50
tons/ha
25
5
55
2.5
2.5
Nutrient
incorporated
into trees/ha
20
4
15
2
45
Total nutrient
consumed
50t/ha
45
9
70
4.5
47.5
Nitrogen
•Nitrogen is a building block of plant protein.
•It is an integral part of chlorophyll and is a component of amino
acids, nucleic acids and coenzymes.
•Most nitrogen in the soil is tied up in organic matter. It is taken up
by plants as nitrate (NO3-) and ammonium (NH4+) ions from
inorganic nitrate and ammonium compounds.
•These compounds can enter the soil as a result of bacterial action
(nitrogen fixation), application of inorganic nitrogen fertilizer, or
conversion of organic matter into ammonium and nitrate
compounds.
•Not all nitrates in the soil are taken up by plants.
• Nitrates can be leached beyond the root zone in sandy soils or
converted to nitrogen gas in wet, flooded soils.
•Nitrogen fixation (from atmosphere) by soil microbes immobilizes
nitrogen, making in available for later use by plants.
Nitrogen Hints
Most plants depend on bacteria to supply nitrogen
Symbiotic Nitrogen Fixation
(bacteria hosted inside roots nodules)
Nitrogen Inputs/Outputs
Agriculture and overall Nitrogen Balance
Nitrogen from Fall to Springtime
Nitrogen Status in Soil in October and March
Nitrate and Leaching
Nitrification and Denitrification
Common N Deficiency
N Deficiencies
Soybean
Rice
Maize
Wheat
Phosphorus
•Plants use phosphorus to form the nucleic acids DNA and RNA and to store
and transfer energy.
•Phosphorus promotes early plant growth and root formation through its role
in the division and organization of cells.
•Phosphorus is essential to flowering and fruiting and to the transfer of
hereditary traits.
•Phosphorus is adsorbed by plants as H2PO4-,HPO4-2 or PO-3, depending
upon soil pH.
•The mobility of phosphorus in soil is low, and deficiencies are common in
cool, wet soils.
•Phosphorus should be applied to fields and gardens before planting and
should be incorporated into the soil. This is especially important for perennial
crops.
• Application rates should be based on soil testing.
P hints
P Deficiencies
Alfalfa
Rice
Wheat
Corn
P Deficiency in Maize and Grape
Potassium
•Potassium is necessary to plants for translocation of sugars and
for starch formation.
•It is important for efficient use of water through its role in
opening and closing small apertures (stomata) on the surface of
leaves.
•Potassium increases plant resistance to diseases and assists in
enzyme activation and photosynthesis.
•It also increases the size and quality of fruits and improves
winter hardiness.
•Plants take up potassium in the form of potassium ions (K+).
•It is relatively immobile in soils but can leach in sandy soils.
•Potassium fertilizer should be incorporated into the soil at
planting or before.
• Application rates should be based on a soil test.
K Deficiencies
Grape
Corn
Alfalfa
Calcium
•Calcium provides a building block (calcium pectate) for cell walls and
membranes and must be present for the formation of new cells.
•It is a constituent of important plant carbohydrates, such as starch and
cellulose.
•Calcium promotes plant vigor and rigidity and is important to proper root
and stem growth.
•Plants adsorb calcium in the form of the calcium ion (Ca+).
•Calcium needs can be only determined by soil test.
•In most cases calcium requirements are met by liming the soil.
•Potatoes are an exception; use gypsum (calcium sulfate) on potatoes to
avoid scab disease if calcium is needed.
•Gypsum provides calcium to the soil but does not raise the pH level of the
soil.
•Keeping pH low helps prevent growth of the bacteriathat cause scab
disease.
Calcium Hints
Magnesium
•Magnesium is a component of the chlorophyll molecule
and is therefore essential for photosynthesis.
•Magnesium serves as an activator for many plant
enzymes required for sugar metabolism and movement
and for growth processes.
•Plants take up magnesium as the Mg+2 ion.
Magnesium Hints
Magnesium Deficiencies
Maize
Cotton
Zinc
•Zinc is an essential component of several enzymes in plants.
•It controls the synthesis of indoleacetic acid (ANA), an important plant growth
regulator, and it is involved in the production of chlorophyll and protein.
•Zinc is taken up by plants as the zinc ion (Zn+2).
•Zinc deficiencies are more likely to occur in sandy soils that are low in organic
matter.
•High soil pH, as inhigh-lime soils, the solubility of zinc decreases and it becomes
less available.
•Zinc and phosphorus have antagonistic effects in the soil. Therefore zinc also
becomes less available in soils that are high in phosphorus.
• Wet and cold soil conditions can cause zinc deficiency because of slow root growth
and slow release of zinc from organic matter.
Zinc
Zinc Deficiencies in Apple
Iron
•Iron is taken up by plants as ferrous ion (Fe+2).
•Iron is required for the formation of chlorophyll in plant cells.
•It serves as an activator for biochemical processes such as
respiration, photosynthesis and symbiotic nitrogen fixation.
•Turf, ornamentals and certain trees are especially susceptible to
iron deficiency (Quince, Peach, Kiwi)
•Symptoms of iron deficiency can occur on soils with pH greater
than 7.0.
•Specific needs for iron can be determined by soil test, tissue test
and visual symptoms.
Mycorrhizae
Most plants have mycorrhizae
Some Plants are Parasitic
Dodder on Pickleweed
Mistletoe on an Oak
Carnivorous Plants
Venus Fly Trap
Round leafed Sundew
Improving Protein Content
Genetic Engineering
There are two main techniques used:
Products of Plant Biotechnology
Delayed ripening tomatoes
Herbicide resistant canola, soybeans, cotton, and other crops
Insect resistant corn, potatoes, and other crops
Golden Rice (vitamin A and beta-carotene enriched)
Plants have hormones
Hormones
Plant Hormones
What is a hormone?
It must meet these criteria:
–
–
–
–
An endogenous organic compound
Active at very low concentrations
Produced in one tissue
Transported from the site of synthesis to the tissue in
which it acts
– Affects growth, development and physiological
responses (it is not a nutrient or vitamin)
Plant Hormones
• Auxin
– Differentiation
– Elongation
– Growth responses
• Gibberellins (GA)
– Elongation
– Cell division
– Seed germination
• Cytokinins
– Cell enlargement
– Differentiation
• Abscisic Acid (ABA)
– Inhibitor
– Responses to stress
– Stomatal opening
• Ethylene
– Fruit ripening
– Flowering
– Flower senescence
• Others
– jasmonic acid,
brassinolide, salicylic
acid
Auxin
• Controls cell elongation and expansion
• Involved in phototropic and gravitropic
responses
– growth of shoots towards light
– downward growth of roots (response to gravity)
• Suppresses growth of axillary buds
• Stimulates root initiation and growth
• Stimulates fruit growth
Phototropism
Phototropism Experiments
More phototropism experiments
Auxin
Effect of Auxin
How does Auxin work?
Terminal Bud Removal
Branching of shoots
• Where do branches
come from?
– Develop from axillary
buds
– Buds are present within
leaf axils on the stem
(stems have buds)
Branching of shoots
• Axillary buds contain a
meristem that is usually
inactive
– apical dominance
growth at the apex
suppresses growth of
lateral shoots
– Why are axillary buds
normally dormant?
Active apical bud
Dormant
axillary
buds
Branching of shoots
• Auxin is produced in
shoot apex and
transported down the
plant stem
– The concentration of auxin
is high close to the shoot
apex
– Auxin concentration is
lower in tissues further
away from the apex
Auxin produced
in shoot apex
High [auxin]
Low [auxin]
Branching of shoots
• High concentrations of auxin
suppress growth of axillary
buds near the apex
• Further away from the apex,
where the auxin concentration
is lower, growth of axillary
buds is not inhibited
• These buds develop and grow,
forming branches
Auxin produced
in shoot apex
High [auxin]
Low [auxin]
Branching of shoots
• The strength of apical
dominance varies among
plant species
– Strong apical dominance
results in plants with a
dominant primary shoot
Branching of shoots
• The strength of apical
dominance varies among
plant species
– Weak apical
dominance leads to a
more branched plant
form
Pinching promotes branching
• Pinching removes the
apical meristem, the
source of auxin
• With no auxin coming
from the apex, axillary
buds develop giving rise
to a bushier plant
Apical bud is removed
Auxin is not present
Axillary buds develop
Tree topping - a (bad) example of
loss of apical dominance
• Tree topping removes
the shoot apex/apices
• Axillary buds grow and
develop into long, weak
sprouts
• Trees that are topped are
permanently damaged
and lose much visual
appeal
Effect of Auxin
Synthetic auxins:
practical applications
• Stimulate rooting of cuttings in
plant propagation
• Control fruit set - the number of
fruit that develop after pollination
• 2,4-D, a synthetic auxin, is used as
a herbicide to kill dicot weeds in
lawns and cereal crops (monocot
plants)
Cytokinins
• Stimulate cell division
• Promote shoot differentiation
• Delay senescence of leaves
Cytokinins
When a terminal bud is removed, the inhibitory effect of
auxin on the lateral buds is removed, and the stimulating
effect of cytokinins activates the axillary buds
Branching of roots
• Branch roots are initiated in the pericycle
• Layer of cells between the endodermis and
vascular cylinder
Secondary growth
• Increased diameter of
stems and roots
• Primarily due to activity
of the cambium
– Layer of meristem cells
between the phloem and
xylem
Secondary growth
• In woody plants,
division of cells in the
cambium gives rise to a
new layer of xylem cells
each year
• Xylem becomes
lignified and permanent,
visible as annual growth
rings
Secondary growth
• Phloem is not a permanent tissue but is
replaced each year
• Cambium provides cells for new phloem
tissue
Manipulating cytokinins
• Promotes shoot growth in tissue culture
• Used to alter fruit shape
Gibberellins (GA)
• Stimulate stem elongation
– many dwarf varieties are gibberellin-deficient
or unable to respond to gibberellin
• Control metabolism of stored reserves
during seed germination
Foolish Seedling
Is a condition found in rice plants where they grow tall and weak, often falling
over and not producing any rice. It is caused by a fungus of Giberella sp.
Gibberellins
They are produced in the tips of shoots and roots, young leaves
and embryos.
Manipulating gibberellins
• Height control - keeping plants small
– flowering pot plants, e.g. Easter lily
– bedding plants
• Increasing size of grapes by making looser
bunches (Thompson seedless)
• Promotes desired elongated shape of 'Red
Delicious' apples
Abscisic Acid (ABA)
•
•
•
•
Stimulates closure of stomata
Promotes maturation and dormancy of seeds
Inhibits seed germination
Regulates many responses to adverse
environmental conditions
– Plants under stress frequently have elevated
levels of abscisic acid
Abscisic Acid
Ethylene
•
•
•
•
Regulates ripening of many fruits
Controls senescence of many flowers
Triggers abscission of leaves and fruits
Increases proportion of female flowers in
cucurbits (cucumber, zucchini, pumpkin)
• Regulates shoot growth during germination
Ethylene
Causes fruit to ripen.
Manipulating ethylene
• Ethylene application
– Stimulates flowering (pineapples)
– Initiates ripening (bananas, tomatoes)
– Promotes fruit drop (cherries)
• Ethylene inhibition
– Delays ripening (long term apple storage)
– Delays flower senescence (silver treatment of
cut flowers)
Summary
• Growth results from
– Cell division
– Expansion or elongation
– Differentiation
• Growth in plants occurs in specialized
areas
– Meristems are the sites of cell division and are
the source of new cells for plant growth
Summary
• Cell expansion and differentiation occur in
regions behind meristem
• Hormones play critical roles in plant growth
• Horticulturists control the shape and form
of plants by manipulating growth and
development
More Uses of Plant Hormones
Gravitropism
Refers to the growth of plants in response to gravity
Sleep Movements
Photoperiod and Flowering
Effect of Red and Far Red Light
Thigmotropism
Manipulating plant growth:
Pruning
• Fruit trees are pruned to develop an efficient structure to
bear fruit and to maximize interception of light
before pruning
after pruning
Manipulating plant growth:
Training
• Plants are trained for both decorative and
practical reasons
Manipulating plant growth:
Shaping
• Trees and shrubs are shaped for commercial
and aesthetic reasons
Christmas trees
Topiary
Two processes at work in plant
growth
At the cellular level there are two processes that
contribute to plant growth
• Cell division
– The source of new cells for growth of an organ or
tissue
division
division
Two processes at work in plant
growth
Cell enlargement
– An increase in the volume of a cell
enlargement
• The combined effects of both processes lead to
the growth of plant organs and to the overall
increase in size of a plant
Primary Growth
• Growth that leads to increased
height of shoots or length of
roots
• Growth occurs at the apices of
these organs
• Cells in the apical meristems
divide and provide the supply
of cells for growth
Cell differentiation
• As cells “move away” from
the apex they differentiate
into specialized types of cells
• Every cell has the genetic
potential to develop into any
of the specialized cell types
in a plant
Differentiation
• Differentiated cells don’t normally
switch to another cell type
• After plant cells differentiate they
are fixed in place
– surrounded by rigid cell walls, glued
together
Manipulating plant hormones
• Horticulturists use synthetic hormones,
hormone analogs and inhibitors of hormone
action to manipulate many aspects of plant
growth and development
• These compounds are called plant growth
regulators