Tempratre related material

2. Topic
Temperature

3.  It is a measure of how hot or cold an object is
compared to another object.
 Temperature as a measure of the average kinetic
energy of the particles in an object
 It is measured by the Thermometer.
Definition:

4.  Temperature is one of the most
important ecological factors.
 It regulates many physiological processes of the plant.
 The metabolic processes are low at a certain minimum
temperature. It increases at particular temperature
called optimum temperature.
 The plant grows best at optimum temperature.
 Metabolism again decreases at maximum temperature.
The plants cannot survive above this temperature
 Both extremely low and high temperatures have
adverse effect on plant growth.
Temperature is an ecological factor

5. Low temperature:
 Low temperature causes cold injuries.
 Water is frozen into ice crystals in the intercellular
spaces.
 It causes injury to cells.

6. High temperature:
 Extremely high temperature cause adverse effects on a
number of vital physiological processes like
respiration, transpiration, protein metabolism etc.
 These effects cause stunting and finally death of
plants. This is called as Heat Injury .
 Different kinds of plants have various ranges of
minimum-optimum-and maximum temperatures.
Plants differ considerably in temperature tolerance.
 Generally, there is little metabolic activity at
temperature below 0°C or higher than 40°C.

7.  Temperature classification of plants
The plants are classified into the following categories
on the basis of temperature requirements.
1. Megatherm:
 The plants live in high temperature throughout the
year are called megatherms. These plants are found in
equatorial and tropical rain- forests.

8.  Mesotherm:
 The plants living at high temperature of summer,
alternating with low temperature of winter are called
mesotherms.
 They are found in deciduous forest of tropical and
subtropical regions.

9.  Microtherm:
 The plants which live in extremely low temperature
are called microtherms.
 It includes plants of temperate and high altitudes
(upto 12000 feet of tropical and subtropical region).
 These regions are dominated by mixed Coniferous
forest.

10.  Hekiskotherm:
 It includes plants of Arctic and Alpine regions • (above
16000 feat in tropics and 12000 feet in temperate) with
very low temperature.
 Alpine vegetation prevails in such locality.

11.  Ecophyiological responses of
temperature
 Temperature is an ecological factor. It affects the rate of
many physiological processes in plants.
 Transpiration:
 Rise in temperature increases transpiration rate. High
temperature influences the saturation deficit of the
atmosphere. It decreases the humidity of air. Thus more
water is transpired. High rate of transpiration also
increases the rate for absorption of water from the soil.

12. Photosynthesis:
 Photosynthesis occurs over a wide range of temperature.
 In some desert plants photosynthesis continues even at
80°C.
 Most of the algae require lower temperature range for
photosynthesis than the higher plants.
 The optimum temperature for photosynthesis for most of
the plants is 25 to 35°C.
 Photosynthesis stops at 40°C in temperate plants and at
50°C in tropical plants

13.  Respiration:
 The rate of respiration increases with the rise of
temperature.
 It is maximum at optimum temperature.
 But it decreases rapidly above optimal temperature.

14.  General distribution of plants:
 Temperature and moisture determine the general
distribution of vegetation.
 Different belts of vegetation occur between the
equator and the poles.
 Vegetation is primarily determined by heat. Thus
plants which grow in a hot climate cannot grow in a
cold climate and vice versa.
 Therefore, same crop are not cultivated in all regions
of the world. Different crops are cultivated in different
region i of the world.

15.  Germination of seed:
 Temperature also affects the germination of seed.
 Every seed has optimal temperature.
 Seed cannot grow below or above this temperature.

16.  Spreading of diseases:
 Temperature and humidity affects the spreading of
plant diseases.
 Low temperature along with high humidity favours the
attack of rust. damping off, seedling blight, foot rot
and root rot.

17.  Changes in the
temperature in the
natural environment of
plants affect both their
functioning and their
growth.
 Maintenance of a
relatively stable internal
environment is just as
important for plant
metabolism as it is for
animals.

18.  Plants respond to changes
in light, water availability
and temperature. All of
which are linked, since
heat is often associated
with light ( for example ,
the radiant energy of
sunlight)

19.  Most Plants have a growth
season and life cycle that
follow the seasonal
temperature variations of
their environment.

20.  Low availability of water
may also be associated
with very cold
temperatures, since frozen
water (ice and snow) is not
available for use of plants.

21.  Temperature above 40* C
may cause damage to
proteins and those above
75* C to chlorophyll
pigment within the plant.
 Since plants can not move
into the shade , they tend to
have stronger physiological
and structural adaptations.

22. Adaptations to extreme
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23.  Reflective leaf surfaces
that reduce the amount
of radiation absorbed
can help keep a plant
cool in hot conditions.
 Leaves may be light or
silvery coloured , or
have waxy or shiny
surfaces.

24.  Evaporative cooling - loss of
water via transpiration
(stomata opening ) in order
to evaporate and have a
cooling effect on the plant.
 This decreases internal
temperature , however
water is not readily available
. This can kill the plant.

25.  Hot areas are often dry,
comprising evaporative
cooling. A plant needs to
strike a fine balance
between the risks of
excess water loss during
cooling versus heat build-
up during water
conservation.

26.  Wilting - Some plants
can wilt during the day
instead, which decreases
surface area of
flowers/leaves to the sun.
 If water is readily
available, this is
temporary.
 If water not available, this
can lead to the death of
the plant. For example,
roses.

27.  Leaf orientation – Plants
change the orientation of
their leaves to decrease
the surface area exposed
to the sun at the hottest
part of the day.
 Most eucalypts hang
vertically to reduce their
exposure to the hot sun

28.  Plants responding to
excessive temperature
like fires, may die,
(especially non woody
plants), however they
leave dormant seeds, with
thick protective seed
coats.
 Seed dispersal in some
Australian plants is
stimulated by the
extreme heat of fire.

29.  Banksia , Hakea and
some Eucalyptus plants
bear fruits with hard
woody cases that are not
dropped from the parent
plant.
 The heat of a fire
stimulates the fruits to
open, and the seeds are
released.

30.  Some of these seeds need
fire as a trigger to germinate
(begin to grow a seedling).
 Or some plants may die
above ground leaving roots,
rhizomes, bulbs or tubers
to survive underground.
When favorable conditions
return, these sprout

31.  Leaf fall in Summer.
Eucalypts are evergreen
trees that drop some of
their leaves during the dry
season in hot climates to
reduce the surface area
exposed to absorb heat.
 This also reduces the risk
of losing too much water
by transpiration.

32.  Temperature is one factor
that controls developmental
changes in a plant’s life
cycle, from germination
through to flowering and
seed dispersal.
 In Australia, too high a
temperature during flower
formation produces a poor
wheat crop, because pollen
formation is very
temperature-sensitive.

33.  Leaf fall in autumn
(deciduous trees)
Many trees lose their
leaves during autumn
and the cold winter
months when resources
(for example the sun and
water) are not as readily
available.

34.  It allows them to survive
not only the extremely low
temperatures, but also the
water shortages and lower
availability of sunlight.
 For example, the beech
tree found in Tasmania

35.  Organic anti-freeze –
Normally, in cold
conditions, water between
cells freezes first posing the
greatest risk of damage for
plants.
 Some plants that live in
extremely cold conditions
produce anti-freeze
substance that reduces the
temperature at which the
cytoplasm or cell sap
freezes.

36.  Frost during periods of new
growth may damage plants,
but many plants have leaves
that are frost-tolerant.
 For example, after frost the
leaves of camellias appear
semi-transparent, but on
thawing return to normal.

37.  Plants may alter their
growth rate, active plant
growth can occur within
the range 5°C-45°C or in
tropical areas, growth may
cease below 15°C.

38.  Vernalisation
some plants flower in
response to low
temperatures for example,
tulip bulbs must be
exposed to between 6
weeks and 3 months of
intense cold before they
will flower.

39.  Australian gardeners often
mimic this effect by
removing tulip bulbs from
the ground in winter and
storing them in the
refrigerator, before
replanting them in spring,
to ensure that they will
flower.

40.  Plants must also maintain a relatively stable internal
environment.
 Since plants cannot move - they tend to have stronger
physiological and structural adaptations.
 For heat some adaptations include wilting and
dropping leaves.
 For cold some include: frost tolerance and being
deciduous.