PLANTS UNDER STRESS

desert

Arid zone

Salty soilAntarctic region

What is Stress?

• A significant deviation from the conditions optimal for life, and eliciting changes and responses at all functional levels of the organism.

• Two ways

Temporary stress

Permanent stress

What Happens During Stress?

How to Recognize Stress

Effects of Stress 1. Stressor-specific effect

involve a well- defined target within the plant.

Ex. Intense radiation causes direct damage to the thylakoidmembrane

2. Non- specific effect Stress responses within the plant is carried out

by phytohormones.

How to Recognize Stress

• Non- specific effects of stress

a. Alterations in membrane properties (membrane potential, transport of substances)

b. Increased respiration

c. Inhibition of photosynthesis

d. Growth disturbances

e. Lower fertility

f. Premature senescence

g. Decrease of availability of energy

How to Recognize Stress

• Intracellular decrease in availability of energy. (Due to metabolic impairment)

• Less ATP is formed.

• It can be calculated as an Adenylate Energy Charge(AEC).

AEC = (ATP)+ 0.5(ADP)

(ATP)+(ADP)+(AMP)

• AEC < 0.6 indicates deterioration in the vitality of a plant, and a plant under stress.

Survival of Stress

• Survival = Stress evasion, Resistance, Recovery

Natural Environmental Constraints

• Environmental stress factors

1. Abiotic factors – mainly include climatic factors.

2. Biotic factors – Due to activity of animals, microorganisms or human beings.

Multiple Stresses

• In nature frequently multiple stresses are involved.

Ex. Stress arise due to combination of strong radiation, overheating, drought in open habitat.

Radiation Stress

• Two ways of radiation stress

1.Excessive quantities of photosyntheticallyactive radiation.

2.increased absorption of UV radiation.

Light Stress

• Strong light presents the leaf with more photochemical energy than can be utilized for photosynthesis.

• Overloading of the photosynthetic process.

• Extremely high irradiance destroys photosynthetic pigments and thylokoidstructures is called “photodamage”

• Shade plants may be damaged breif exposure of strong light.

Light Stress

Conostomum tetragonium exposed to the high light intensity

Photoinhibition

• Inhibition of photosynthesis caused by excessive radiation.

• Strong light attack photosystem II

• Brake down of Protein sub units

• Photosynthetic electron transport is interrupted.

• Reduce efficiency of photosystem II

Photoinhibition

As an protective measure,

• Excessive radiation energy is diverted to fluorescence and heat.

• Surplus reductive capacity in chloroplast is used by “Xanthophyll Cycle”

Xanthophyll Cycle

Thylakoid membraneLumen Stroma

A moss quenches high light energy with the pigment zeaxanthin.

a) Pellia endiviifolia did not experienced a rise in de-epoxidized Xanthophyll.

Liverworts

b) Flullania dilatata was a rise in the concentration of de-epoxidized xanthophylls that can protect cell from chlorophyll damage

a)

b)

Adaptation to Stress from Strong Light

• Positioning leaves at an angle to the incoming light- Receive less radiation.

• Rolling up the shoots (mosses, pteridophytes) • Dense coverings of trichomes on the upper

surface of the leaf. • Thickened walls in the epidermis and hypodermal

tissue-act as diffusive filters (conifer needles & cacti)

• Presence of Anthocyanin- act as darkening filters & shields the mesophyll.

Ultraviolet Radiation

• Two types of UV radiation

UV-A (315-400nm)

UV-B (280-315nm)

• UV-A is mainly photooxidative.

• UV-B is in addition to photooxidative action causes photolesions in biomembranes.

UV Damage

• Breaking down the disulfide bridges in protein molecules.

• Dimerizing thymine groups of DNA- results in defective transcription.

• Xanthophyll cycle is disrupted by inhibiting the violaxanthine-deepoxidase

UV Damage

Can be identified by

• Changes in enzyme activity (increased peroxidase activity, inhibition of cytochromeoxidase).

• Poor energy status of the cell.

• Lower photosynthetic yield.

• Disturbed growth (reduced extension growth & pollen tube elongation).

PLANT STRESS DUE TO EXTREME TEMPETURES

24

KINETIC ENERGY OF MOLECULES= HEAT

KINETIC ENERGY OF MOLECULES

HIGH ENERGY

LOW ENERGY

HEAT

COLD

25

Temperature balance on earth by,Solar radiationair current

Heat and Cold effect• Metabolic activity• Growth• Viability • Distribution,

of a plant.

26

Critical temperature Thresholds

• Activity limit

(5-25 0C)

• Lethal limit

– Cold

– Heat

27

28

Heat

Highest temperature on earth- 80oC

Lethal limit- 40-70oC

High temperatures arise by,

• Higher solar radiation

• Volcanic phenomena

• Hot pools

• Fires

29

Functional disturbance of heat

• Damage physiochemical state of bio membranes and the conformations of protein molecules.

– Disturbance in photosynthesis

– Disturbance in transport

– Disturbance in mitochondrial respiration

30

Heat Tolerance

• Evasion of strong sunlight– Thick cutine layer

• Heat insulating bark– Thick fibrous bark– Rough suberized bark– Silica in cell walls– Peripheral cambium layer

• Dense leaf sheaths covering the basal buds• Withdrawal to underground organs• Transpirational cooling

31

Most effective form of heat protection is provide by,

Heat shock proteins

32

Type of heat resistance

Three types

• Heat sensitive species

• Relatively heat resistant eukaryotes

• Heat tolerance prokaryotes

33

Cold

lowest temperature on earth= -90oC

Lethal limit= +5 - -90oC

low temperatures arise by,

• Low solar radiations

34

Functional disturbance of cold

Above the freezing pointBy Decrease the speed of chemical reactions

• Uptake of water and nutrients restricted

• Less metabolic energy

• Less biosynthesis

• assimilation reduced

• Growth stops

35

The first main detectable result of low temperature is,

cessation of cytoplasmic streaming

36

Mostly effect on chilling sensitive plants. It happens in stepwise

37

Primary effect:-LIQUID CRYSTALINE BIO MEMBRANES → SOLID GELL

Initial reversible processes:-DAMAGE TO THE FUNCTIONALITY OF ORGANS

CLOROPLAST- INHIBIT PHOTOSINTHESISMITOCHONDRIA- INCREASE RESPIRATION

Final irreversible processes:-INSUFFICIENT CARBOHUDRATES

IMPAIRED ION BALANCEIMBALANCE IN METABOLISM

ACCUMILATION OF TOXIC SUBSTANCESINJURY AND DEATH OF CELLS

Type of chilling sensitive plants

• Partially sensitive plants

• Totally sensitive plants

38

Below the freezing pointFROST OCCUR PERIODICALLY AND EPISODICALLY ON EARTH

by the ice formation

• Cytoplasm destroy by ice crystals

• Block the vascular bundles

• Ice nucleation active bacteria attack

39

By ice formation less water in the plant = Desiccation condition arise

40

It results,

• Unfrozen solution reach abnormally high concentration

• Toxic effect

• Enzymes get inactive

• Bio membranes are overtaxed both osmotically and by the volume reduction

41

Freezing of cells

• intercellular • Extracellular

42

Low temperature tolerance• No thermal insulation (no heat losses)

– Dense growth surrounding the regenerative buds

– Giant rosette

• Abscission of sensitive organs

• Depression of freezing point

• Super cooling

• Trans located ice formation (extra tissue freezing)

43

Categories of cold resistance

• Chilling sensitive plants

• Freezing sensitive plants

• Freezing tolerance plants

44

EVOLUTION OF VASCULAR PLANTS FOR FROSTHappen in a stepwise process

45

First step:COLD ADAPTATION OF ENZYMES AND MEMBRANES

Second step:IMPROVING THE SUPERCOOLING CAPACITY

Survival capacity

• Younger plants are more sensitive

• Reproductive organs are more sensitive

• Underground organs are also quite sensitive

• Above ground shoot is the least sensitive part

46

Winter desiccation

Winter conditions may result in damage due to desiccation.

This happen by,

• Frozen soil

• Snow and ice

47

Effects of winter desiccation

• Plants can not take up enough water and nutrient

• Loss water by stomatal transpiration

• Xylem transpiration make cavities of the water columns in the conducting vessels

• Block the passage of water through the xylem

• Chronic damages in plant tissues

48

Harmful effect of long periods beneath ice or snow

• Low CO2 and O2 permeability of ice sheets

• Stop the gas exchange of plant

• Respiratory CO2 increase and O2 decrease with in the plant

• Hypoxia

• Toxic substances accumulate

• Pathogenic effect

49

Oxygen Deficiency in the Soil.

Drought

Salt Stress

Oxygen Deficiency in the Soil.

Lack of sufficient oxygen in the soil.

Extensive areas of land are temporarily inundate by

flood waters of large rivers, small rivers or streams

repeatedly overflow their banks.

the plants cover of valley soils is often buried of long

period of times.

Soils are compacted and become impermeable as a result

of construction activities.

The soil atmosphere is low in Oxygen in any

case,

Anaerobic microorganisms take over .

Creating a strongly reducing milieu which Fe2+ ,Mn2+

, H2S, Sulphides ,Lactic acid ,Butyric acid are present in

toxic concentration.

Nitrogen turnover in the soil.

Functional Disturbances and Patterns of

Injury

roots are capable of respiring anaerobically,

continuous for some hours irregularities in metabolism

occur.

partial pressure of Oxygen drops to 1-5 kPa (Hypoxia)

Alternative respiratory pathway is activate.

The energy status of the adenylate system drops

substantially.

Root growth stops.

Root tips entering the low Oxygen zone die off

Adventitious root developed.

Older part of the root systems often develop corky

intumescences and swollen lenticels.

Total and near total Oxygen deficiency (anoxia)

Respiration switches to anaerobic dissimilation

In the absence of terminal oxidation

Acetaldehyde and ethanol accumulate.

Abscisic acid, ethylene and ethylene precursors are

formed in larger amount.

Evoking in the leaves partial stomatal closure.

Epinasty and often abscission.

Cellular membrane systems brake down.

Mitochondia and microbodies disintegrate and their enzymes

are partially inhibited.

Fig. 6.51

Surviving Oxygen Deficiency

Many plants can germinate, roots and grow in oxygen deficient

soil because they have developed certain adaptations to meet

conditions in an toxic environment.

Functional adaptation Morphological

adaptation

Functional adaptation

increase in alcohol dehydrogenase (ADH) during

anaerobiosis.

Protein metabolism is adjusted within a few hours

after gene activation

Morphological adaptation

A hypoxic milieu consist in the development in ventilating

tissue (aerenchyma) with a continuous systems of

intercellular spaces.

The volume of intercellular system in the root parenchyma,

swamp plants – 20%-60%

well-aerated plant – <10%

Well aerated roots may even loss oxygen to the surrounding

soil, It can detoxify harmful reducing substances :

Fe2+ Fe111- oxide.

Aeration is also furthered by temperature gradients.

Plants growing on very dense and poorly aerated soils develop

a system of laterally spreading roots near the surface.

In the flooded regions submerged parts of trunks and

branches put out dense bundles of water roots.

poplar, willow, alder, ash

In mangrove plants,

In the form of lenticels-covered respiratory roots

(pneumatophores) with a large amount of aerenchyma.

Knee roots that produced above the surface of the soil and

standing water.

Drought

A period without appreciable precipitation, during with the

water content of the soil is reduced to such an extent that

plants suffer from lack of water.

Low precipitation and high evaporation.

Strong evaporation caused by dryness of the air and

high levels of radiation.

The dry region of the earth

Functional disturbance and patterns of Injury

Decrease in turgor and a slowing down of growth process

Decrease in cell volume

Most strongly inhibited enzyme is nitrate reductase.

plants that have been treated with nitrogen containing

fertilizer in drought.

Nitrogen fixation is more sensitive to drought.

Increase in concentration of the cell sap.

Progressive dehydration of the protoplasm

Protein metabolism and synthesis of amino acids are

impaired.

Supresses cell division

Slow down mitosis- S phase being affected most.

During pollen development, the meioses exhibit

chromosome anomalies- specially metaphase and anaphase.

Drought lower pollen fertility.

During drought,

Initiate stomatal closer

Under the influence of hormone synthesized in the

leaves and roots in response to drought

Changes occur in the allocation of assimilates

The ratio of shoot to roots growth is altered

Characteristic morphogenetic features develop

Reproductive processes become predominant

Senescence is accelerated

Older leaves dry out and shed

In wilt,The reduction of cell volume

Increasing concentration of the intercellular solutes-ions

In the final phase preceding cellular disruption

The central vacuole splits up into small fragmentary

vacuoles

The thylakoids in the chloroplasts and the mitochondrial

cristae first of all swell and are later break down

The nuclear membrane becomes distended and the

polyribosome disintegrate

Drought stress in tobacco

Fig. 6.62

Survival of Drought

Drought resistance

the capacity of a plant to withstand period of dryness, and is

a complex characteristics.

xerophytes

Desiccation Avoidance

desiccation is delayed by all those mechanisms

that enable the plant to maintain a favorable tissue water

content as long as possible despite dryness of air and

soil.

uptake of water from the soil

reduced loss of water

Water uptake

extensive root system with a large active surface area is

improved further by rapid growth into deeper soil layer

the seedling of woody plants in dry regions may have

tap roots ten times as long as the shoot

grasses in such places develop a dense root system and

send their threadlike roots to depths of some meters.

Fig 6.64

Reduction of transpiration

Modulative adptation

timely closure stomata

when leaves growing under conditions of water

deficiency develop smaller but more densely distributed

stomata.

Fig 6.65

The leaves have more densely cutinized epidermal walls

Covered with thicker layer of wax.

Stomata are present only on the under side of the leaves

smaller

often hidden beneath dense hair or in depression

Boundary layer resistance is increased and the air outside the

stomata become moisture

Rolling the leaves

Salt stress

Salt stress may have be a first chemical stress

factor encountered during the evolution of life on earth.

Saline habitats

the presents of an abnormally high content of

readily soluble salt

Aquatic saline habitat: Oceans, salt lakes, saline ponds

In land: saline soil

Effect of high salt concentration on plants

The burden of high salt concentrations for plant is due to

osmotic retention of water and to specific ionic effect on

the protoplasm.

An excess of Na+ and Cl- in the protoplasm lead to

disturbance in the ionic balance

Ion specific effects on enzyme protein and

membrane.

Too little energy is produced by photophosphorylation

and phosphorylation in respiratory chain

Nitrogen elimination is impaired

Protein metabolism is disturbed

Accumulation of diamines such as putrescine

cadaverine,polyamines

Functional disturbance

Photosynthesis is impaired

Stomata closure

Effect of salt in chloroplast in particular on electron

transport and secondary process

Respiration increased or decreased – root

Enzyme system of glycolysis and the tricarboxylic acid

cycle are more sensitive than alternative metabolic

pathways.

When the NaCl content of the soil is high the uptake of

mineral nutrients NO3- , K+ , Ca2+ is reduced.

Extreme salt stress

Inhibition of root growth

Bud opening is delayed

Shoot are stunted

Leaves are small

Cell die and necrosis appear in roots, buds, leaf margins and

shoot tips

The leaves become yellow and dry before the growing

season has ended and whole portion of the shoot dry out.

Lower level of cytokinin

Increased abscisic acid senescence

Survival of Saline habitats

plant growing in saline habitat cannot evade the

effects of salt and must therefore develop at least some

degree of resistance to it.

Salt resistance is ability of a plant either to avoid,

salt regulation

excessive amount of salt from reaching the

protoplasm

to tolerate the toxic and osmotic effect associated

with the increased ion concentration.

Regulation of the salt content

1. Salt exclusion: In some mangrove- transport barriers of the

roots prevent the salinity of the water in the conducting

system from becoming too high.

Prosopis farcta

crop plants

halophorbic species

2. Salt elimination : A plant can rid itself of excess salt ,

releasing volatile methyl halides –

exclusion by glands

excretion of salt at the shoot

shedding parts heavily loaded with salt

marine phytoplankton

macro algae

fungi

3. Salt redistribution:

Na+ and Cl- can be readily translocated in the

phloem , so that the high concentration arising in actively

transpiring leaves can be diluted by throughout the plant.

4. Salt tolerance : the protoplasmic compartment of

resistance to salt stress.

Anthropogenic stressMan made pollutants and their impact on the phytosphere.

Due to human activities plants exposed to greater amounts of harmful substances.

Human activities…

• Results of industrial processes.

• Traffic.

• Chemicals used in agriculture and household, fertilizers, pesticides.

• Excessive consumption of fossil fuels-emmission of green house gases.

• Catastrophic accidents-nuclear reactor activities, oil spills.

• Pollutant

A contaminant of air, water or soil that has an adverse effect on an organism.

1.Naturally occurring pollutants

2.Anthropogenic pollutants

Instead of one pollutant activity combined activity of pollutants.

Ex: Photo oxidant complex + SO2 (g),+ heavy metals

Naturally occurring harmful substances in higher concentrations.

• SO2 (g),NO2 (g),H2S (g),O3 (g)

• Dust.

• Heavy metals.

Ultimate result is environmental stress.

Ecosystems

Countries

Continents

Entire globe

• High input of pollutants within a short period of time = acute damages

• Exposure to low concentrated pollutants for a longer period of time = Chronic damage

Pollution Injury

The extent which vital(physiological & biochemical) functions are affected.

Visible damage depend on many factors of the plant.

1. Plant species.2. Growth form.3. Age of the plant.4. Phase of activity.5. General vigour(physical strength & good health.6. Climatic and edaptic condition.7. Chemical nature.8. Concentration of the pollutant.9. Time and duration of the action of the pollutant.

Air born pollutants

• SO2 (g),NOx (g), PAN (peroxyacetylnitrate),Hydrogen helides, NH3(g), hydrocarbons, tar fumes, soot, dust.

Symptoms of damage

• Non specific.

• Many symptoms interact with other plant stress factors.

• At noon stomata are fully open atmospheric pollutant concentration is high in noon damage is higher.

• At night plants recover from the injurious immisions.

Early recognition of pollution damage1. Accumulation of toxic compounds/substances in the

plant tissues.2. Reduction of buffering capacity of tissues.3. Erosion of epicuticular wax .4. Decreation /incretion of certain enzyme activities.5. Qualitative and quantitative shifts among

metabolites.6. Appearance of stress hormones– Ex: ethylene7. Respiration incretion/decreation8. Photosynthetic disturbance.9. Alteration of stomatal opening and closure.10. Diminished allocation of photosynthetes to the root

system.

When the pollutant in immediate vicinity..

1. Occurrence of chlorosis.

2. Leaf discoloration.

3. Tissue necrosis.

4. Death of entire plant.

•Reduce productivity and defective fertility.

•Less growth in cambial tissues.

•Foliage become sparser.

•Water transpiration interfered.

SO2 (g) –cause most of the damage

Natural sources-volcanic emissions, S containing ores, biological decay and forest fires.

Man-made sources-fossil fuel combustion, smelting, manufacture of sulfuric acid.

SO2 (g) is there in the environment since the plants beginning.-Plants have been adapted to tolerate SO2 (g) for some extent.

Entry into plants.

1. Enter the leaf through opened stomata.

2. By over-coming the cuticular resistance.(if the stomata are closed)

Damage by SO2 (g)

SO2 (g)

low external concentration

Trigger a loss of turgor in epidermal cells

Stomata open

Transpiration high

• High external concentration

• Stomata closure

• Low transpiration

• SO2 (g) diffuse similar as CO2 (g) .

Atmospheric SO2 (g)

Dissolved in guard cell wall water SO2 (g) +H2O(l)

HSO3-(aq) + SO3

2-(aq)

Chloroplast: Cytosol: Vacuole96 : 3 : 1

Sulphur compounds (SO2(g),H2S (g) )detoxification

01.) SO32-

(aq) SO42-

(aq)

SO32-

(aq) remaining will effected by the photosynthetic sulphur metabolism

Covert to sulphur containing amino acids.(cysteine, methionone)

Call wall peroxidases.

Harmful effects of SO2 (g)

1. SO32-

(aq) Level in chloroplast rise.

2. SO2(g) ,occupies binding sites in RUBP carboxylases.

secondary process of photosynthesis inhibits.

3.The tertiary structure of the enzymes are disturbed.

4. SO32-

(aq) SO42-

(aq)

Super oxide radicals generate, if not excluded rapidly chlorophyll will be destroyed.

photooxidation

Mechanisms of resistance of SO2 (g)

stress* can be passive or active processesPassiveNon specific, not usually related

to a particular pollutant.1. Regular development of new

leaves with short functional life span.

Ex: deciduous

woody plants

• Thallophytes also have structural, chemical characteristics reduce the entry of SO2

ActiveStressor specific processes.1. High buffering capacity-from

increased uptake of alkali & alkali earth cations.

2. Binding to 2ry products of metabolism.

3. Metabolic use of Sulphur and detoxifying oxidative reactions.

4. C4 syndrome.

Ever green trees with needles

Ever green tree s with needles Deciduous woody plants

C4 syndrome

C4 grass

1.Miscanthus sinensis

2.Andropogon virginicus

Moderate resistant C3

1.Polygonaceae

2.Metrosideros collina in Hawaii

Some plants have the ability to grow in the vicinity of volcanic vents

Species-specific sensitivity to immissions.

• Different species

• Individual varieties and ecotypes

• Different life stages

SO2 (g) Resistant plant species introduce to

polluted areas.

Highly sensitive plants to SO2 (g) Indicator organisms to indicate SO2 (g)

pollution.

Atmospheric oxidants and secondary photooxidants.• O3(g) ,NOX(g) (NO(g) ,NO2(g)),peroxy radicals.

• NO2(g) NO(g) + O.(g)

• O. (g) + O2 O3(g)

• NO(g) + O3(g) NO2 (g) + O2(g)

Peroxy radicals +hydro carbon compounds

UV 300-400 nm

Peroxyacetyl nitrtes.Peroxybutyl nitrates.Peroxybenzyl nitrates.

Uptake by the plant

• Through opened stomata.

• NO2(g) diffuse through cuticle, much faster than SO2(g) .

• O3 (g) dissociate to O2(g) in the outer wall of the epidermis.

• NO(g) ,NO2 (g) NO3-(aq) ,NO2

-(aq) with water

taken up actively by living cells

Events within the cell.

• NO3-(aq) amino acids.

* SO2 (g) inhibit the action

of Nitrite reductase.

• Additional source of nitrates-advantageous.

• Acidification of cells/leaves-disadvantageous.

Nitrite reductase enzyme

Toxicity of nitrates

O3(g)

• O3(g) O2(g) + O.

• Peroxides,

-effect on plasma membrane.

-other bio membranes.

Transfer process impaired.

Necrosis,growthreduction,lessyields

Heavy metal contamination of soil, water

Create long term problems

metals = Zn,Pb,Ni,Co,Cr,Cu

Metalloids = Mn,Cd,Se,AS

Accumulation in organisms, circulate in food chains.

Common heavy metal sources1. Industrial zones.

2. Heavy vehicle traffic.

3. Sewage sludge.

4. Emissions of dust from metal processing industries.

5. Waste water-Cd,Zn,Fe,Pb,Cu,Cr,Hg

Uptake and toxic effects

• Uptake is mainly by roots.

-can’t stop the enter of heavy metal completely.

-need to plants as micro elements.

Toxicity due to..

1. Interference with electron transport in respiration an photosynthesis.

2. Inactivation of vital enzymes.

Possible mechanisms of resistance • Natural heavy metal exposures, plants growing on,

a. Metal ores.

b. Serpentine soils.

c. Strongly acidic soils.

Adaptations.

1. Immobilization in cell wall.

2. Obstruct permeation across the cell membrane.

3. Formation of chelates.

4. Compartmentalization in vacuoles.

5. Active export.

6. Characteristic patterns of iso-enzymes-element specific resistance.

7. Genetic plasticity, with several resistance genes-resistant to several heavy metals.

*these plant can be used to re-vegetation of strongly heavy metal contaminated area.

Ex:

Agrostis tenuis Festuca ovina Silene vulgaris

Bioindicators of pollution impact

• Bioindicators are organisms or communities of organisms that are sensitive to pollution stress and respond by alteration in their vital processes or by accumulation of the pollutant.

Bioindicators

•Indicator organisms- respond to their surroundings, depending on their specific requirements

•Test organisms- high degree of sensitivity to certain pollutants.

•Monitor organisms- specific responses to pollutants can be con be used for qualitative & quantitative detection of stress situations.

Indicator organisms

Accumulation of heavy metals influenced by ..1. Meteorological factors

2. Edaphic factors -Influenced by the soil rather than by the climate.

3. Habitat related factors- growth form and rooting pattern.

Heavy metal indicators= metallophytes.

Ex: Eichhornia crassipes

Reasons for forest decline

1. Ageing of the stand.

2. Episodic damage by pests.

3. Extremes of climate.

4. Inappropriate management.

5. Interruption of mineral recycling.

6. Exhaustion of soil nutrients.

7. Toxicity caused by identifiable local emitters.

forest decline

• Depend on the,

1. Tree species.

2. Growth form.

3. The site.

4. Type of the soil.

5. Geological origin.

6. Superimposition of various stress types.

Symptoms of forest decline

1. Anomalous growth.

2. Discoloration of needles and leaves.

3. Necrosis of isolated areas of needles, leaves, branches.

4. Shedding of leaves.(thinning of crown, bareness of the hanging branches).

5. Dieback of leader and branch tips.

6. Increasing the shallowness of the root system.

Causes of forest decline.

• Acidic effect of precipitations.

Direct acid damage1. necrosis of margin of leaf

2. destruction of the cuticle and cuticular waxes.

3. acidification of the apoplast– affect the distribution of phytohormornes.

4. fine root chromosome anormalities during cell division.

5. cells damage dissolution of cell walls tissue disruption.

Effect of atmospheric pollutants on the ecosystems and at the global level.

1. Acid precipitations

Green house effect

• provides temperature necessary to support the life on earth.

• Green house gases

1. CO2(g)

2. H2O(g)

3. CH4(g)

4. O3(g)

5. N2O(g)

Green house effect

References:1. http://www.hindawi.com/journals/jb/2012/872875/

(15.10.2012)

2. http://lqma.ifas.ufl.edu/Publication/BB-02.pdf (15.10.2012)

3. http://www.hokkaido-ies.go.jp/seisakuka/acid_rain/Acidrain-e.html (15.10.2012)

4. Larcher W., Physiological plant ecology, 3rd edition,Springerpublications,Berlin. pp 321-449.