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Global warming and its impact on
productivity
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INDEX
Evolution of atmosphere with respect to different eras
Sequence involved in climate change
Concept of Productivity
Physiological changes in plants under temperature stress
Mitigation strategies to cope climate change
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Aeon Era Duration in
millions of
years
Millions of
years ago
Phanerozo
icCenozoic 65 5
Mesozoic 183 248
Palaeozoic 295 543
Precambrian
Proterozoic Late 357 900
Middle 700 1600Early 900 2500
A
rchaean Late 500 3000
Middle 400 3400
Early 400 3800
Hadean 800 4600
Table 1: Geologic time-scale showing major climatic and evolutionary eventsduring the Precambrian Era
rise of atmospheric oxygen (ice age)
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Elements Theoretical reducingatmosphere
Present oxidizingatmosphere
CarbonMethane (CH4)Carbon Monoxide (CO)
Carbon Dioxide (CO2)
Hydrogen Hydrogen (H2) Water (H2)
NitrogenAmmonia (NH3)Nitrogen (N2)
Nitrogen (N2)
Oxygen Water (H2O) Oxygen (O2)
Table 2. Forms of elements in early and present atmosphere.
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Climate change :
Statistically significant variation in either the mean state of the climate or
in its variability, persisting for an extended period (typically decades or
longer).-----
MOEF.
Global Warming:
Global Warming refers to an average increase in the Earth's temperature,
which in turn causes changes in climate patterns.
Green House Gases:
Carbon dioxide (CO2), Methane (CH4), Nitrous oxide (N2O), Hydro
fluorocarbons (HFCs), Per fluorocarbons (PFCs) ,Sulfur hexafluoride
(SF6)
Green House effect:
The greenhouse effect is an increase in the temperature of a planet as heat
energy from sunlight is trapped by the gaseous atmosphere
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Morphological changes Anatomical changes
Scorching of leaves and twigs Sunburns on leaves, branches
and stems Leaf senescence and abscission
Shoot and root growth inhibition Fruit discoloration
Reduced cell size Closure of stomata and curtailed
water loss Increased stomatal and
trichomatous densities Greater xylem vessels of both
root and shoot Mesophyll cells were damaged
in grapes.
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Physiologicalchanges
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High leaf temperature and water deficit lead to heat stress
CAMplants
Stomataclosed (Day)
No cooling byTranspiration
Re emitted by conductionconvection
Loss of heat
a) Soil water deficit
b) High relative humidity
4 to 5 0C increase leaftemperature
C3 andC4 Plants
Stomataopen (day)
C3 and C4Plants
Stomatapartial closed
Cooling of leaf temperature
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Photosynthesis is inhibited before respiration at hightemperature
At normal condition, rate of photosynthesis is more than rate of
respiration.
Temperature at which rate of photosynthesis equals rate of respiration
is called as compensation point.
At temperatures above compensation point, rate of respiration is more
than the rate of photosynthesis.
Under such condition photosynthesis cannot replace the carbon used
as substrate for respiration.
As a result carbohydrate reserves decline, and fruits and vegetables
lose their sweetness.
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High temperature reduces membrane stability
At high temperature, there is a increase in the fluidity of membrane
lipids which results in loss of physiological function.
High temperature decreases the strength of hydrogen bonds and
electrostatic interaction between the polar groups of proteins within
the aqueous phase of the membrane.
Modification of membrane composition, structure and leakage of
ions.
Inhibition of processes such as photosynthesis and respiration that
depend on the activity of membrane associated electron carriers and
enzymes
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Several adaptation to protect leaves against excessive heating
Plants avoid excessive heating of leaves by lowering the
absorption of solar radiation.
Reflective leaf hairs and leaf waxes.
Leaf rolling orientation and growth of small, highly dissected
leaves.
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At high temperatures plant produce heat shock proteins
Book source :Plant Physiology (Taiz & Zeiger) p 605
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Adaptation to heat stress is mediated through cytosolicCalcium
Book source :Plant Physiology (Taiz & Zeiger) p 606
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Accumulation of
compatible osmolytes
sugars and sugaralcohols (polyols),proline, tertiary andquaternary ammoniumcompounds, andtertiary sulphonium
compounds
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Mitigation strategies for plants to cope up with climate change
To identify the varieties sensitive to high temperature.
Improved thermotolerance using various genetic approaches.
Induction of Thermo tolerance.
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Accumulation of compatible osmolytes:
sugars and sugar alcohols (polyols), proline, tertiary and quaternary
ammonium compounds, and tertiary sulphonium compounds areaccumulated .
Secondary metabolite production:
Increased activity of Phenylalanine ammonia-lyase -main acclimatory
response of cells to heat stress.
Thermal stress induces the biosynthesis of phenolics and suppressestheir oxidation-acclimation to heat stress in watermelon.
anthocyanins serve to decrease leaf osmotic potential -increased uptake
and reduced transpirational loss of water under environmental stressesincluding high temperature
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CONCLUSION
Climate change is a serious concern which canaffect overall productivity of crops plants andnatural vegetation.
Effects of high temperature on plants range frommorphological, anatomical and physiologicalchanges.
It is important to study plants responses to heatstress in order to understand their mechanism to
cope with high temperature.
It is possible to induce thermo tolerance in plantsthrough gradual exposure to heat.
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REFERENCES
Book of Plant Physiology (Taiz & Zeiger)
A. Wahid, S. Gelani a, M. Ashraf a, M.R. Fooladb(2007) , Heat tolerance in plants: An overviewEnvironmental and Experimental Botany 61 199
223.
Jenks M.A and Hasegawa P.M (2005) Plant abioticstress (1th ed) Blackwell Publishing Ltd. Oxford. UK.
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