3. Definitions
The physiological process by which the
excess water is lost from the living
tissues of plants in the form of vapor is
called transpiration.
Transpiration is the process of water
movement through a plant and its
evaporation from aerial parts, such as
leaves, stems and flowers.
Transpiration is the process by which
water vapour leaves the living plants
body and enters the atmosphere.
(Michel,1978)
4. According to recent studies it has be revealed that about 10 % of the moisture
found in the atmosphere is released by plants through transpiration. The
remaining 90% is mainly supplied by evaporation from, ocean, seas, lakes, rivers,
streams etc.
During dry periods, transpiration increase the loss of water in the upper layer of
soil, which effect vegetation, horticultural and agronomic field crops.
Plant transpiration is pretty much an invisible process.
Transpiration is the evaporation of water from plants and trees.
Approximately 90% of all water taken up by a plant is lost to transpiration.
Characteristics
5. Transpiration is the final step in a continuous water pathway that starts
from the soil, into plant roots and ends as it passes into the atmosphere.
98% of a plants energy is used in the work of transpiration
Transpiration rates are highest in leaves.
Transpiration is an elegant, sustainable natural design that performs its
vital functions without electricity, without fossil fuels and without moving
parts
Many xeric plants have small leaves, silvery reflective leaves, hairy leaves
and/or produce essential oils which are all strategies to reduce
transpiration by reducing evaporation.
Characteristics
6. • Transpiration is a very useful procedure for plants-
oIt creates negative pressure gradient that helps draw water
and minerals up through the plant from its roots.
oHelps to keep the plant cool on hot weather- a method of
evaporating cooling.
oSupports photosynthesis and encourages the exchange of
gases, helping maintain levels of CO2 and O2 in the
atmosphere.
Importance of transpiration
7. • It also plays an significant part in Global Hydrological Cycle-
oReleases approx 10% of water back in to the environment.
oProduces 90-450 kg of water for each pound of solid material produced
by plants.
oCreates water vapor that forms into fog and clouds. Transpiration is also
the reason why there is higher humidity in places with lots of vegetation
cover
oTranspiration through plant stomata is the main pathway for water
entering the atmosphere over land.
oTo a water resources person, transpiration is considered a loss to the
watershed. If plants could somehow use less water, the amount saved
would remain on the ground to increase recharge
importance
8. • On the basis of the passages through which plants give out water
in the form of vapor transpiration is of three types:
Stomatal
transpiration
Cuticular
transpiration
Lenticular
transpiration
Types of transpiration
9. • Stomatal transpiration:
• Transpiration that occurs through
stomata called stomatal
transpiration. This type of
transpiration only occurs in its
presence of sunlight (in daytime).
Because stomata open in the
present of sunlight and close in
the darkness. In this method
plants give out 80-90% water in
the form of vapor.
Types of transpiration
11. • Cuticular transpiration:
Transpiration that occurs
through the cuticle or cracks of
thin cuticle layer of leaves and
stems is said to be cuticular
transpiration. This is a day-night
process. In this process, 5-10%
water is given out in the form of
vapor.
Types of transpiration
12. • Lenticular transpiration:
Sometimes transpiration occurs
through lenticels, the small
opening in the corky tissue
covering stems and twigs, and
this type of transpiration is said
to be the lenticular
transpiration. In this process,
only 0.1% water is given off of
the forms of vapor.
Types of transpiration
13. Aerial parts
of whole
young plant
Lenticels
(lenticular
transpiration)
0.1%
Cutin
(cuticular
transpiration)
3%~10%
Stomatum
(stomatal
transpiration)
~ 90%
Types of transpiration
17. Water is passively
transported into the
roots and then into the
xylem.
The forces of cohesion
and adhesion cause the
water molecules to
form a column in the
xylem.
Water moves from the
xylem into the
mesophyll cells,
evaporates from their
surfaces and leaves the
plant by diffusion
through the stomata.
Mechanism of transpiration
18. Mechanism of transpiration
It involves three basic steps
• Absorption at the roots.
• Capillary action in the xylem vessels.
• Evaporation at the leaf.
19. Roots absorb water from the soil through
osmosis.
Water travels from high concentration
area to low concentration area via a
semi-permeable membrane called
osmosis.
Cell water concentration < soil water
concentration.
Absorption
20. why not soil molecules enter?
Active Transport Passive Transport
Requires cellular
energy.
Does not require
cellular energy.
It circulates from
lower concentrated
areas to the higher
concentrated areas
It circulates from the
higher concentrated
areas to the lower
concentrated areas
Absorption
23. Turgor Pressure exerted by fluid in a cell that
presses the cell membrane against the cell wall.
Turgor is what makes living plant tissue rigid.
Loss of turgor, resulting from the loss of water
from plant cells, causes flowers and leaves to wilt.
Turgor pressure
24. • The rate of loss of
water from the plant is
greater than the
absorption of water in
the plant
Wilting
26. • Adhesion occurs when water
forms hydrogen bonds with
xylem cell walls.
• Cohesion occurs when water
molecules hydrogen bond
with each other.
• Cohesion between water
molecules creates a “water
chain” effect.
Capillary Action
30. • Water potential quantifies the tendency of free (not bound to
solutes) water to move from one area to another due to osmosis,
gravity, mechanical pressure, or matrix effects such as surface
tension.
Water potential
34. • Lack of water in soil
• Reduce the number of leaves
• Turn the leaves into spine
• Leaf---spine
stomata—less number of stomata—
reduce transpiration
Example: cactus
Adaptation & Distribution
Xerophyte plants
36. Cold climate and Deciduous
• Shedding of leaves
Reduce transpiration
Deciduous tress shed twice a year
Adaptation & Distribution
37. Cold climate and Evergreen trees
• Reduce surface area of leaves
• Decrease surface area into needle like structure
• Reduce number of stomata
• Reduce transpiration
example-pine
Adaptation & Distribution
38. Equatorial Evergeen
• Bigger leaves,big surface,lot of stomata
• Thik waxy layer known as cuticle
• Cuticle cover the stomatal opening in epidermis
• Prevent excessive loss of water
• Help to limited amount of transpiration
• Ex-banana leaf
Adaptation & Distribution
39. Not having waxy layer
• Having sunken stomata
• Cover with lots of hair
• Fine fibrous structures covers the stomatal opening
• Traps the vapor that come out to stomata
• Humidity increase into it
• Reduce transpiration
• Ex: nerium oleander
Adaptation & Distribution
40. Stephen Hales (1972) devised three methods for measuring the rate of
transpiration:
1. By weighing potted plants
2. By potometer
3. By measuring the humidity of air
Measurement Of Transpiration
41. By weighing potted plants
• Record decrease
of weight over 3
hours
• Amount of water
loss from the
leaves
Measurement Of Transpiration
45. By Measuring the Humidity of Air
This method can be used for measuring the rate respiration from single
leaf. The leaf is enclosed in plexiglass chamber and sealed. Air is passed
through the chamber at a definite flow rate. The humidity of the air
before entering the chamber and after leaving the chamber is
measure.
Amount of water transpired= Relative humidity ( after closing the
chamber) – Initial relative humidity of chamber
Measurement Of Transpiration
46. Thornthwaite then derived an equation to provide evaporation estimates based
on a series of observed evaporation measurement
The first part of the Thornthwaite estimation technique (Thornthwaite, 1944,
1954) derives a monthly heat index (i) for a region based on the average
temperature t (°C) for a month
Thornthwaite equation of evapo-transpiration
48. Factors that affect
transpiration rate of
plants are smeared in
two ways-
Plants Parameters
Environmental
Conditions
Factors Affecting Transpiration
49. • Plants Parameters:
Stomata: When stomata are open, transpiration rates increase; when
they are closed, transpiration rates decrease.
Number of Stomata: More stomata will provide more pores for
transpiration.
Number of Leaves: More leaves mean a bigger surface area and
stomata for transpiration.
Factors Affecting Transpiration
50. Cuticle: The thicker the cuticle layer on a leaf surface, the slower the
transpiration rate.
Leaf Area (Transpiring Area): A plant with large leaf area will show
more transpiration than another plant with less leaf area
Root/Shoot Ratio: A low root/shoot ratio decreases the rate of
transpiration while a high ratio increases the rate of transpiration.
Factors Affecting Transpiration
51. Mesophyll: Compact mesophyll reduces transpiration while a loose
mesophyll increases transpiration.
Leaf Modifications: Formation of prickles, leaf spines, scaly leaves,
phyllodes, phylloclades, are all modifications found in xerophytes to
reduce transpiration.
Factors Affecting Transpiration
52. Environmental Conditions:
Light intensity:
• it warms the leaves up quicker.
• It also cause the stomata to open,
thus more transpiration occurs
during the day and the rate is higher
on a sunny day compared to a cold
dull day.
Factors Affecting Transpiration
53. Humid atmosphere
• At low humidity there is a lower
concentration of water molecules in
the air around the leaves. This
concentration gradient helps the
transport of water molecules from
the leaves by diffusion.
• High humidity means the air around
the leaves is already saturated and
has a higher concentration of water
molecules than inside the leaves.
Factors Affecting Transpiration
54. Temperature:
An increase in the air
temperature warms the water
inside the leaves more quickly
causing it to evaporate quicker. It
also increases the capacity of
the air to absorb more water.
ROT
Factors Affecting Transpiration
55. • Wind:
Transpiration relies on diffusion. Windy
conditions cause the air molecules to be
blown away from the leaves, preventing
the air around the leaves becoming
saturated with water molecules.
• Soil Water
Factors Affecting Transpiration
56. • Meteorology is a branch of the atmospheric sciences which includes
atmospheric chemistry and atmospheric physics, with a major focus
on weather forecasting.
Hydrometeorology is a branch of meteorology and hydrology that
studies the transfer of water and energy between the land surface and
the lower atmosphere.
Hydrometeorology is the science which deals with the movement of
water and water vapour in the atmosphere
Hydrometerology
