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 ofthe 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 LeavesThe 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

Wheat

Rice

Maize

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

Corn

Wheat

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

Alfalfa

Corn

Calcium

• Calcium provides a building block (calcium pectate) for cell walls and membranes and must be present forthe 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 metby 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 pHlevel of

the soil.• Keeping pH low helps prevent growth of the bacteria that 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 in high-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 BiotechnologyDelayed 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

Dormantaxillary 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 producedin 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 producedin 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 removedAuxin is not presentAxillary 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 SeedlingIs 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

GravitropismRefers 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

• The combined effects of both processes lead to the growth of plant organs and to the overall increase in size of a plant

enlargement

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