The document discusses the significance of temperature in plant physiology and ecology, highlighting its impact on growth, reproduction, and metabolic processes. It elaborates on how plants adapt to varying thermal environments through mechanisms like frost hardening and morphological changes. Additionally, it categorizes plants based on their temperature requirements and stresses the direct relationship between temperature and the distribution of plant species.

1. Course Title:
Plant Physiology and
Ecology
Course Instructor:
SALMAN SAEED
Botany department
UNIVERSITY college of management & Sciences, Khanewal,
PAKSITAN

2. 2
Salma
Saeed
Lecturer
(Botany)

3. 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.
3
Salma
Saeed
Lecturer
(Botany)

4. TEMPERATURE AS AN ECOLOGICAL
FACTORS
1. 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.
4
Salma
Saeed
Lecturer
(Botany)

5. CONT.
6. Temperature varies in :
 Space.
 Time.
 Altitude.
 Latitude.
 Wind, water.
 Vegetation cover.
5
Salma
Saeed
Lecturer
(Botany)

6. 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.
6
Salma
Saeed
Lecturer
(Botany)

7. 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.
7
Salma
Saeed
Lecturer
(Botany)

8. IMPORTANCE OF TEMPERATURE FOR 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.
8
Salma
Saeed
Lecturer
(Botany)

9. 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.
9
Salma
Saeed
Lecturer
(Botany)

10. TEMPERATURE AND PHYSIOLOGICAL
PROCESSES
iii.
a) 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.
Plants die at 50°c.
iv. High temp. kill protoplasm.
10
Salma
Saeed
Lecturer
(Botany)

11. 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.
11
Salma
Saeed
Lecturer
(Botany)

12. 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.
12
Salma
Saeed
Lecturer
(Botany)

13. 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.
13
Salma
Saeed
Lecturer
(Botany)

14. 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.
14
Salma
Saeed
Lecturer
(Botany)

15. PLANT PHYSIOLOGICAL RESPONSES & 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.
15
Salma
Saeed
Lecturer
(Botany)

16. 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.
16
Salma
Saeed
Lecturer
(Botany)

17. 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.
17
Salma
Saeed
Lecturer
(Botany)

18. 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.
18
Salma
Saeed
Lecturer
(Botany)

19. 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.
19
Salma
Saeed
Lecturer
(Botany)

20. 20
Salmanbotanist@gmail.com