SUBMITTED TO: DR NOOR ZAMAN.

“WATER FACTOR , TEMPERATURE FACTOR AND WIND FACTOR.”

Submitted by : Samra Marrium

(13131506-012) Botany 7th

The Water Factor

WATER CYCLE IN NATURE Water exhibits cyclic flow between

atmosphere , land and sea , and between living organisms and their environment referred as water cycle or hydrological cycle.

Without cycling of water ecosystem could not function , and life could not maintained.

Watre cycle is characterized by :1. Precipitation.2. Interception.3. Infilteration.4. Evaporation.

STAGES OF WATER CYCLE1. Precipitation: It results from condensation of water vapours

derived from surface of oceans. It is the major source of soil moisture and driving force of the water cycle.

Precipitation begins as water vapour in atmosphere . When the air rises it is cooled and when it rises above the temperature level at which condensation take place ,clouds form.

The condensing moisture aggregate to droplets , when diameter reach about 1mm ,they fall as rain.

CONT.2. Interception: As the precipitation reach earth , some water

reaches ground directly , some is intercepted by vegetation and by building etc.

Because of interception various amount of water evaporates into atmosphere without reaching the soil surface.

3.Infilterartion: The precipitation that reaches the soil moves

in to ground by infilterartion. More intense the rain, greater would be the infiltration.

CONT. Water seeps down and called gravitational

water. A great amount of water is used by humans and

for domestic purposes. A part of water is held in soil by capillary forces

between the soil particles called capillary water.4.Evaporation: Water on the surface of ground, on the surface of

vegetation, and in stream, lakes and oceans return to atmosphere by evaporation.

Some water is lost by roots of plants . The total loss of water from the surface of ground

is called as evapotranspiration.

ATMOSPHERIC MOISTURE Water exist as :1) Invisible vapour (humidity).2) Visible vapour (cloud and fog).1. Humidity:i. The actual amount of water vapours in

atmosphere is known as absolute humidity.

ii. It is measured in ounces per cubic yard or grains per cubic foot of air.

iii. It differs from place to place.

CONT.iv. It declines if we move from equator (20mm) towards

pole (1mm).v. The percentage of moisture present in atmosphere as

compared to its full capacity is called relative humidity .It is defined as “percentage of maximum quantity that the air can hold at a temperature “.

vi. Temperature governs humidity .warm air can hold more water than cold air. The capacity of air carrying vapours become double with increase of 11°c.

vii. Relative humidity is low during day and high in night.viii. In rain forests low relative humidity is 80% and in

desert it may be below 10%.

CONT.2. Cloud and fog :i. It consist of water droplets or some

sometime ice crystals formed from cooling of air to a temperature below its dew point.

ii. They differ in their locations.iii. Clouds are separated from earth while fog

is present near the earth. When further cooled both converted to droplets.

iv. Clouds are formed when air moves upward from land surface into colder regions of atmosphere.

CONT.v. Fog is formed by warm air passing over

cold water currents in the sea , by warm air rising up a sloping land surface to high elevations , and by rapid cooling of land surface during night.

MEASUREMENT OF RELATIVE HUMIDITY PSYCHROMETER The most common instrument is used to

measure relative humidity is called psychrometer.

It Consist of pair of thermometer, bulb of one thermometer is covered with cloth, cloth is wetted, then thermometers are whirled in air.

Temperature of wet bulb is lowered compared to dry one. Dry bulb indicates true temperature and relative humidity is read by means of two temperatures .At 100% relative humidity , both temp. are identical.

IMPORTANCE OF ATMOSPHERIC MOISTURE TO PLANTS 1. Effect on intensity of solar radiations: Vapour in atmosphere intercept with solar

radiations, before it reaches the earth hence less energy is available for photosynthesis and respiration. E.g. slow growing dwarfed trees.

2. Effects on evaporation and transpiration:

With the increase in relative humidity ,reduces the rate of evaporation and transpiration and vice versa.

CONT.3. Source of soil moisture : When fog moves horizontally, or clouds come

in contact with earth , minute water droplets deposits as they pass through foliage and absorbed by soil.

4. Direct use by plants : Mosses and lichens absorb moisture from

humid atmosphere without waiting for condensation. When relative humidity rises above 85%, epiphytes and xerophytes absorb water directly.

PRECIPITATION Precipitation is condensation of water

vapours in the form of rain ,hail and snow etc.

It is source of soil moisture. It is major driving force of water cycle as

well. Precipitation directly or indirectly affects the

plant life through humidity and water content of the soil , therefore important ecological factor.

TYPES OF PRECIPITATION It has three major types :1.Cyclonic precipitation.2.Orographic precipitation.3. Convection precipitation. 1. cyclonic precipitation: It is caused by eddies of warm air several

hundred miles in diameter rising in vertical spirals about centers of low atmospheric pressure. These storms moves easterly along the edge of cold polar air masses that cap both northern and southern hemisphere.

CONT. As the ascending mass of air in cyclone

rises, it expand , mingles with cold air , greatly cooled , and precipitation result from this phenomenon.

2. orographic precipitation:

It caused by currents of air rising over an elevation, expansion and cooling cause precipitation.

3.CONVECTION PRECIPITATION It occurs in summer, air next to ground is

heated and density is lowered as compared to upper atmosphere . It moves upward vertically to altitude where it is chilled to condensation point and bring down rain.

FORMS OF PRECIPITATION Normally precipitation takes three forms

given below:1. Snow: When condensation takes place under very

low temperature ( below 32°F) the moisture released after condensation is frozen in the form of hexagonal crystals called snow.

2. Hail and steel: Sometime drops become solidified in to

small rounded piece of ice called hail. The falling snow or hail mixed with rain is

steel.

CONT.3. Rainfall: Clouds consist of millions of tiny water

droplets .when clouds become older the droplets coalesce to form large drops, reach certain size , and fall out as rain.

It is determined by:a) Geography.b) Pattern of air movement.

MEASUREMENT OF PRECIPITATION. Rainfall is measured in inches or millimeters. Measured by rain gauge. Simple rain gauge consist of funnel with

vertical collar around rim of funnel which collects water .the volume of water can be measured by pouring in to graduated cylinder. And a calibrated stick is inserted to measure collected water.

Daily rainfall is measured then monthly rainfall is taken by average of daily rainfall.

CONT. The mean annual rainfall is derived from the

mean of monthly rainfall.

IMPORTANCE OF PRECIPITATION TO PLANTS1. Snow: It may be injurious or beneficial. Snow that melt is a source of water. By wind and by rain break off tree

branches. At high altitude and latitude it damage

vegetation. Snow press seedlings down-may attacked

by fungus easily.

CONT.2. Rainfall: Source of moisture for soil. Helps to crack open thin skinned fruits e.g.

cherries and tomatoes and release seeds. The amount of rain determine vegetational

zones e.g. Subtropical forests ,rain forest etc.

3. Hail and steel: Cause damage to aerial parts of plants.

DROUGHT AND DROUGHT RESISTANCE OF PLANT DROUGHT It can be defined as : “an extreme

fluctuations from the mean rainfall (less than 75%) at certain place on particular area” .

Xerophytes and succulents are adapted to water stress.

If rainfall is far enough below than normal, it badly effects vegetation. This is referred as drought. Drought leads to:

Reduction in size. Reduction in yield and vigour. Leads to death.

CONT. When dry season is accompanied with higher

temperature, that causes the plants to use up soil moisture very rapidly, promoting the effects of drought.

plant response to drought: plants exhibits responses to drought

variously such as :i. In some plants leaves curl , in other these

wilt , or stomata closed.ii. Prolonged drought inhibit production of

chlorophyll so leaves turn yellow.

CONT.iii. Deciduous trees may shed leaves

prematurely.iv. Water stressed plants reduce osmotic

potential due to accumulation of ions calcium, sodium, magnesium in leaves.

v. Conifers and evergreen species- winter drought –browning of needles and die back of twigs from dehydration.

PLANT ADAPTATIONS TO DROUGHT Plants in arid and semi arid regions have

evolved adaptation to survive and reproduce in drought .These include :

1. Reduction in leaf area of canopy: Plants drop their leaves and reduce leaf

area canopy, and develop new leaves at the onset of rainy season .

It affects photosynthesis but it is compensated by green stem.

CONT.2. Change of angle of leaves: When water is limited , plants reorient leaves

so surface is parallel to sun rays and reducing the transpiration and evaporation.

3. Succulence: Development of fleshy tissues for storage

and retention of water in plant body are called succulent plants e.g. cacti .they absorb water in rainy season and use this water in dry season.

CONT.4. Leaf adaptations: Various leaf adaptations:a) Small leaves .b) Cell walls thickened.c) Stomata modified.d) Palisade tissues are more developed.e) Vascular system denser.f) Coated with waxes and resins.

CONT.5. Root adaptations:a) Deep roots can reach underground water.b) Spreading shallow root- cover large area.6. Ephemerals life cycle: Seeds germinate quickly- bloom and

produce seeds before moisture gone- drought escapers –survive as dormant seed.

7.Halophytes: Have salt secreting glands and leaves

coated with waxes.

ECOLOGICAL CLASSES OF PLANTS BASED ON WATER RELATIONS1.Hydrophytes: It include aquatics which normally grow in

water. Presence of spongy tissues. Presence of air spaces. Phytoplanktons , Floating

(wolffia) ,Submerged (Elodea , Emergents (typha).

CONT.2. Xerophytes: Plants live in dry habitat. Complete life cycle in short duration. Succulents contain water storing tissues. E.g. cacti.3. Mesophytes: Plants can not inhabit water or wet soil and

soils where water is depleted.

The Temperature Factor

HEAT AND TEMPERATURE All organisms live in a thermal environment

is characterized by heat and temperature. Heat is form of kinetic energy possessed by

all substances due to random motion of molecules of that substance.

Temperature is direct measure of heat .it expresses intensity of hotness and tendency to give up heat.

TEMPERATURE AS AN ECOLOGICAL FACTORS1. Most important factor.2. It affects growth and reproduction of plants.3. Little biological activity below 0°c and

above 50°c.( below 0°c due to water immobilization and above 50°c protein denatures).

4. They can grow and reproduce only in a narrow range of temperature, optimum temperature.

5. They maintain their their heat by reradiation, convection, and transpiration.

CONT.6. Temperature varies in : Space. Time. Altitude. Latitude. Wind, water. Vegetation cover.

PLANTS AND THERMAL ENVIRONMENT Plants are fixed at place so they can not

move hence they have to experience wide range of temperature .

Their roots, crown, stem has to experience different temperature in day.

Internal temperature is influenced by environment.

They maintain their heat by reradiation, convection, and transpiration.

FROST HARDENING Plant can tolerate extremes of cold by frost

hardening i.e. formation or addition of antifreeze compounds in roots, shoots, and leaves and hence lower the freezing point through super cooling.

IMPORTANCE OF TEMPERATURE TO PLANTS 1. Temperature and metabolism: It affects metabolic processes of plants by

influencing the kinetics of chemical reactions and effectiveness of enzymes.

Transpiration, photosynthesis, respiration are effected by temperature , for every 10°c increase in temperature metabolic rate is doubled.

2. TEMPERATURE, GROWTH AND REPRODUCTION Plants can grow and reproduce with in narrow

range called optimum temperature. Each part of life cycle require different

temperature e.g. temperature necessary for germination is lower than the , temperature that favors flower development.

Optimum temperature vary among species, and among individuals in population.

TEMPERATURE AND PHYSIOLOGICAL PROCESSESa) Heat stress: Heat affects physiological processes of

plants .This is called heat stress and it cause :

i. Photosynthesis declines.ii. Shut down normal protein synthesis.iii. Plants die at 50°c.iv. High temp. kill protoplasm.

B) COLD STRESS When temperatures drops below minimum

for growth of plant. Plant become dormant and photosynthesis and respiration slows down called cold stress. it leads to:

i. Chlorosis.ii. Precipitation of proteins.iii. Freezing of water.iv. Viscosity of water is doubled.v. Cracks in shoots hence vulnerable to

parasitic fungi into living tissues.

TEMPERATURE AND DISTRIBUTION OF PLANTS The temperature limits the ranges of plant

species directly or indirectly. Temperature in combination with moisture

determines the distribution of vegetation. Temp. is maximum at equator and decrease

gradually towards poles hence vegetation is maximum at equator.

In addition to temperature rainfall, topography, soil and geology also important in determining distribution of plants.

CONT. The successive zones of vegetation from

base to upward :a. Tropical.b. Subtropical.c. Temperate.d. Alpine. Aquatic habitat is divided to:a. Epilimnion: Zone –vertical gradient of

decreasing temperature.

CONT.b. Thermocline or metalimnion: Short zone-

rapidly falling temperature.c. Hypolimnion: Bottom cold zone where no

temperature gradient. Temperature and plant diseases: The ability of parasitic fungi to enter and develop

with in host organisms depends upon temperature below 13°c , the seedling of maize are susceptible to diseas.

PLANT PHYSIOLOGICAL RESPONSES AND ADAPTATIONS TO TEMPERATURE Plants have developed a number of

morphological and physiological adaptations during extremes of temperature :

1. Formation of dormant bulbs and tubers.2. Sun leaves of oaks are smaller and have

deeper lobes than shade plant increasing surface area for cooling.

3. Desert plants develop small leaves to avoid transpiration.

4. Plants resist to extreme temp. by forming thick walled spores.

CONT.5. In some plants osmotic concentration

increases that prevent freezing point .Increase in osmotic value enhances amount of bound water in colloidal form e.g. in winter rye leaves and stems are flexible at very low temperature.

6. Cacti are succulents have high level of bound water and high cytoplasmic viscosity.

7. Removal of water from vacuoles- no water to freeze in cold e.g. dry seeds are able to germinate even after exposure with -190°c for three weeks.

CONT.8. Dormancy helps seeds in overwintering.

Similarly aestivation that occurs during summer help to resist high temp.

9. Certain plants when exposed to rise in temp. ,produce heat shock proteins.

10. Plants obtain resistance to chilling and frost damage by insulation. E.g. the internal temperature of rosette plant is 20 °c higher as compared to outer temperature.

ECOLOGICAL CLASSES OF PLANTS BASED ON TEMPERATURE Raunkiaer divided the gross vegetation

into following groups :1. Megathrms:The plants that live in warm

habitats – found in tropical areas and desert etc.

2. Mesotherms: These are found in tropical and sub tropical and can with stand intermediate temp.

CONT.3. Microtherms: The plants that require low

temperature for their growth are called microtherms – found in tropical and sub tropical at high elevations.

4. Hekistotherms :These are plants of cold and alpine regions .they can with stand very long and severe winters.

The wind Factor

WIND Air in motion is called wind. It is important factor on flat plains , along sea

coasts, at high altitude in mountains. It affects plants directly by increasing

transpiration, by delivering heat to relatively cool leaves, by causing various kinds of mechanical damage, and by scattering pollens and disprsal of seeds and fruits.

EFFECTS OF WIND ON PLANTS Carbon dioxide replenishment: Wind removes bound layer of still air that

covers the surface of shoot preventing the diffusion of O2 from stomata and carbon dioxide towards stomata.

1. Cooling: The bounded layer accumulates heat by

conduction over epidermis .wind thins this layer, cause cooling of leaves.

CONT.2. Desiccation: Air in motion causes evaporation rapidly

thus increasing rate of transpiration. This results in desiccation because of removal of water from the tissues killing the leaves and twigs.

3. Dwarfing: Turgidity helps the maturing cells of plant to

normal sizes. The plant develop under influence of drying winds never attain turgidity. As result all organs are dwarfed.

CONT.4. Deformation: When developing shoots are subjected to

strong wind pressure from a constant direction , the form and the position of shoot may become permanently altered. This is called deformation. Trees with inclined trunks are observed on ridges.

5. Lodging: It is a form of injury caused by violent wind in

which crop plants flattened against the ground. But if stem is not mature ,plant become

partially erect once.

CONT.6. Breakage: Wind promote breakage in plants. Trees with soft and brittle wood are more

susceptible to breakage. High wind uproot the trees.

Single or group of trees which are uprooted in a forest are termed as wind falls or wind throws.

CONT.7. Abrasion: Wind carrying particles of ice or soil is

very potent abrasive force. Bark and buds may be eroded away .Crops grown on sandy soil are often damaged in this way.

8. Wind pollination (Anemophily): In cool and cold climates the vast

majority of trees , shrubs and herbs are wind pollinated.

CONT.9. wind dispersal (Anemochory): Wind is efficient dispersal agent and most

terrestrial plant depend on it to scatter their disseminules ( seeds and fruits). The fruits and seeds have developed certain adaptations for wind dispersal such as smaller size and reduced weight , production of wings and hairs so that they carry by wind easily.

CONT. Seeds and fruits of certain plants have

developed specialized ‘mechanism such as tumbling, catapult mechanism etc’ are dispersed by wind.

ANEMOMETER Wind is measured by anemometer. Robinson anemometer. It consist of three or four arms –arms fixed to

vertical shaft operates gears motivating a dial.

Average velocities can be taken . This provide a much more useful index of

velocities.