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Plant Adaptations

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Plant Adaptations Plants can survive in many extreme environments. In order to survive in such environments, these plants need to have adaptations. – PowerPoint PPT presentation

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Title: Plant Adaptations


1
Plant Adaptations
  • Plants can survive in many extreme environments.
  • In order to survive in such environments, these
    plants need to have adaptations.

2
Shelfords Law of Tolerance
  • Organisms are constrained by both the maximum and
    minimum extremes of an environmental condition
    thus these extremes represent the limits of
    tolerance.
  • The response curve for an individual to
    increasing levels of an environmental resource is
    a bell-shaped curve.
  • The growth/response of an organism best within a
    specific range of conditions.
  • As these conditions get further from the optimum
    (too high or too low) so growth diminishes

3
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4
Warming (1909), on the basis of amount of water
present in the soil, plants were classified into
FOLLOWING groups.
  1. Hydrophytes plants that occur in water e.g.
    Hydrilla, Pistia, Lemna, Wolffia etc.
  2. Mesophytes those plants which prefer to grow in
    the habitats that are neither too dry nor too wet
    i.e. moderate amount of water. Which means the
    oxygen supply to root is also moderate. Those
    plants are unable to grow in wet and damp soils.
  3. Xerophytes - plants adapted to a dry habitat
  4. Helophytes plants that occur in marshy places.

5
  • 4. Oxylophytes- plants growing on acid soils
  • 5. Halophytes plants growing on saline soils
  • 6. Psychrophytes plants occurring on cold soils
  • 7. Lithophytes- plants growing on rocks and
    stones
  • 8. Psammophytes plants occurring on sand and
    gravels.

6
1. Hydrophyte Adaptations
  • Have lots of air spaces in their tissues.
  • This helps them to float in water.
  • stomata are on the upper surface and have a
    cuticle on the upper surface to exchange the
    gases.
  • These plants have a very thin cuticle if submerged

7
1. Hydrophyte Adaptations
  • Roots in water-clogged soil are called Breathing
    Roots or Pneumatophores.
  • These roots grow to reach the surface above the
    water in order to obtain CO2 to survive.
  • Marshes or Swamps

8
Hydrophytes pictures
9
Hydrophytes pictures
10
2. Xerophyte Adaptations
  • 1. Well established root systems.
  • Grow deeply and in all directions in order to
    anchor the plants in sandy soil and against the
    wind.
  • Helps to maximize water uptake.

11
1. Xerophytes possess adaptations to prevent
excessive water loss
  • 2. Sunken stomata
  • creates local humidity/decreases exposure to air
    currents
  • 3. Presence of hairs
  • creates local humidity next to leaf/decreases
    exposure to air currents by reducing flow around
    stomata
  • 4. Fewer stomata
  • decreases transpiration as this is where water
    is lost
  • 5. Thick waxy cuticle
  • makes more waterproof impermeable to water due
    to the high heat and intense sunlight.

12
Xerophytes possess adaptations to prevent
excessive water loss
  • 6. Short Life Cycles
  • Grow from seeds to mature plants, produce
    flowers, fruits and seeds in a short amount of
    time.
  • These few days can coincide with the few days of
    rain.
  • 7. Many desert plants are called C4 or CAM
    (Crassulacean acid metabolism) plants.
  • These plants only open their stomata in the dark
    at night.
  • The cooler temperatures allow the plant to take
    up CO2 through their stomata without sacrificing
    water.
  • Examples orchids, cactus, pineapple (CAM)
    crabgrass, corn (maize) sugarcane (C4)

13
Transverse Section Through Leaf of Xerophytic
Plant
14
Xerophytes pictures
15
Xerophytic Plants
16
3. Halophytic Plants
17
3. Halophytes
  • 80 of the earth is covered by saline water
  • Very few plants are able to tolerate saline
    conditions without serious damage
  • Plants that survive in saline environments are
    termed halophytes
  • Most halophytes prefer saline conditions but can
    survive in freshwater environments
  • Most halophytes are restricted to saline
    environments

18
What is a halophyte?
  • Plants capable of normal growth in saline
    habitats and also able to thrive on ordinary
    soil (Schimper, 1903).
  • Plant which can tolerate salt concentrations over
    0.5 at any stage of life (Stocker, 1928).
  • Plants which grow exclusively on salt soil
    (Dansereau, 1957).

19
Halophyte picture
20
Halophyte picture
21
Comparison between hydrophytes, xerophytes and
halophytes and their adaptations
1. Morphological features.
Hydrophytes Xerophytes Halophytes
Leaves The submerged leaves are thin, much dissected while aerial leaves are large, entire or slightly lobed. Leaves Leaves may be thin or rigid, fleshy and leathery. Leaves Leaves are thick and their surfaces are reduced.
22
Hydrophytes Xerophytes Halophytes
Stem There are well developed creeping underground stems (rhizomes) with profuse adventitious roots embedded in the mud. The stem is soft and tender Stem Stem is aerial, mostly erected but with limited growth. The stem is rigid and stout. Stem Well developed aerial stem and much branched. The stem ranges from soft to hard woody type.
23
Hydrophytes Xerophytes Halophytes
Roots No elaborate root system occurs. No root systems develop in totally submerged hydrophytes. Roots Large elaborate root system occurs. Roots are mostly tap roots penetrating great depth of soil. Roots Tap root system is not much elaborate and deeply penetrating. In many cases, roots are negatively geotropic.
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2. Anatomical features
Hydrophytes Xerophytes Halophytes
Plants surfaces are not coated with any waxy or hairy coverings. Plants are coated with waxy and hairy outgrowths. Similar to xerophytes.
No development of cuticle. Plant organs are well cuticled. Like xerophytes.
25
Hydrophytes Xerophytes Halophytes
Stomata are either absent or when present they are restricted on the upper surface of leaves. Stomata are not sunken. Stomata are sunken and they are present on the lower surface of the leaves only. Stomata are either sunken or lie at near the level of the lower spidermis.
Stems and other plant parts are traversed by air cavities to maintain buoyancy. Air cavities are absent, instead present hypodermal water storage tissues. Like xerophytes.
26
Hydrophytes Xerophytes Halophytes
The xylem and other woody lignified tissues are poorly developed. Xylem and lignified tissues are highly developed. Lignification of woody tissues is extremely poor.
Mechanical tissues extremely reduced or not at all developed. Development of mechanical tissues with extensive lignification does occur. Mechanism tissues are less developed.
Glandular hairs and many types of secreting plant organs do not occur. Various types of glandular hairs and secretory organs are present. Secretory organs are found to be present in many plants.
27
3. Physiological features
Hydrophytes Xerophytes Halophytes
Rate of transpiration is less. Removal of water takes place by guttation. Rate of transpiration is decreased or entirely checked by heavy cutinisation of epidermis and by the formation of sunken stomata. Like xerophytes, the rate of transpiration is checked by various kinds of morphological and anatomical modification of leaves.
The growth rate of submerged plants is reduced due to weak light intensity. The growth rate of plants is slow due to maximum utilization of carbohydrates in the formation of cell wall. The growth rate of plants is normal.
28
Hydrophytes Xerophytes Halophytes
Gases exchange of submerged organs with the atmospheric air takes place by air communicating system through stomata. O2 and CO2 present in the air cavities are used in respiration and photosynthesis respectively by internal circulation. Gases exchange of both aerial and underground plant parts with the atmosphere takes place normally. Gases exchange of the aerial plant parts takes place normally but the respiration of underground parts i.e. roots take place by the formation of negatively geotropic roots known as pneumatophores.
29
Hydrophytes Xerophytes Halophytes
Absorption of water and mineral salts takes place by the entire permeable plant surface under water. Absorption of water and mineral salts takes place by the help of long-seated root system. Absorption of water and mineral salts takes place slowly and selectively by the elaborate root system.
30
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