Plant Phy siology & Ecology
B.Sc. (Hons) III Semester
Plant Adaptation
Plant adaptations to different growth conditions - where does it fit?
Core Standard: Observe, describe, and ask questions about structures of organisms that affect their growth
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O b s e r v e, c o m p a re, a n d r e c o r d t h e p h y s i c a l characteristics of live plants f r o m w i d e l y d i f f e r e n t environments, and describe how each is adapted to its environment.
Overview
ü What all plants have in common....
ü The major climate zones and plant adaptations to them
ü A hands on exercise with insect-eating plants
Plants
plants All require nutrients
C, H, O, P, K, N, S, Ca, Fe, Mg
Water, air, soil sunlight
What plants differ in
ü Most plants grow in a much wider range of conditions (e.g. in botanical gardens) than we find them in nature, but this only works if we shield them from competition
ü in nature plants differ in exactly what kinds of conditions they grow best in relative to their competitors
ü And: plants differ in what other things they do that give different species unique advantages
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Last question
Why do climate zones often still differ even though they are on the same latitude ?
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Rainforests and the
tropical climate zone
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Climate adaptation in real plants
Please examine the plants that are before you
Which climate might these plants be adapted to?
ü What features might allow them to cope particularly well with the climatic conditions in their respective habitat?
I. List of plant adaptations to tropical climates
ü Large dark-green leaves (= lots of chlorophyll) to absorb sun light, especially in understory with lots of shade ü leaf arrangement maximizes light capture
ü slick waxy cuticle to allow rain to run off
ü shallow roots (no need to go deep for nitrogen or water) and buttress or stilt roots (to help with stability)
10 ü epiphytic life style (orchids, bromeliads, ferns, cacti etc.)
allows to be near sun light; soil not that ü great anyway, aerial roots instead
ü many climbing plants (lianas, strangler figs, rattan, etc.) ü continuous growth (no year-rings in trees); trees can
reach enormous height
II. List of plant
adaptations to
desert climates
ü Sun avoidance and tolerance; small leaves or no leaves at all to minimize water loss
ü photosynthesis instead often in trunk
ü leaves frequently modified to spines which aid in defense but also can reflect excess light
ü “accordion trunk” to reduce sun exposure
ü special CO2 capture mechanism (C4/CAM) to minimize water loss while absorbing CO2
ü highly reflective cuticle to reflect excess light ü dense hair to generate isolating boundary layer ü extremely seasonal growth and reproduction
ü long lived, must be able to skip years if seasons don’t allow
ü succulence; storing of water in specialized tissues (fleshy leaves, trunks, underground etc)
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III. List of plant adaptations to temperate climates
ü annual life cycle
ü deciduousness when perennial
ü if not deciduous then leafs are needles protected by thick cuticle to survive winter
ü thick bark to protect against cold winters
Types of Xerophytes
1. Ephemerals or Drought Escapers
The plants live for a brief period during the rains. The rest of the years is passed in the form of seeds.
e.g., Euphorbia prostrata, Tribulus terrestris
2. Annual or Drought Evaders
The plants live for a months even after the stoppage of rains. For this they have modification to reduce
transpiration.
e.g., Echinops echinatus, Solanum surattense
Types of Xerophytes
14 3. Succulent or Drought Resistance
The plants have fleshy organs where water and mucilage are stored. Depending upon the organ where succulence occurs, the succulents show
ü chylophylly (fleshy leaves, e.g., Aloe, Agave) ü chylorhizy (fleshy roots, e.g., Asparagus)
ü chylocauly (fleshy stems, e.g., Opuntia, Euphorbia)
Types of Xerophytes
4. Non-succulent Perennial Xerophytes or Drought Endurers
They are true xerophytes which actually tolerate drought conditions. Leaves are often small, vertical, thick and leathery. They have either reflecting surfaces (e.g., Nerium) or possess a coating of hairs (e.g., Gnaphalium, Aerua).
Types of Xerophytes
They live in abundance of water with at least their lower parts (roots etc.) and leaves immersed water.
Roots of hydrophytes are poorly developed/completely absent in Wolffia, Ceratophyllum etc. roots are poorly branched (e.g., Pistia); roots hair absent or poorly developed. Root cap absent but rot pockets may be present (e.g. Eichhornia, Pistia, Trapa).
Hydrophytes
Types of Hydrophytes
1. Free floating
e.g., Wolf fia (smallest Angiosperms), Pistia, Eicchornia, Azola, Salvinia
2. Submerged
I. Suspended e.g., Utricularia, Hydrilla, Najas II. Rooted e.g., Vallisneria, Elodea, Potamogeton
16 3. Emerged or rooted floating
Fixed at the bottom of water body by well developed roots but leaves/ shoot are partly /completely aerial.
With floating leaves e.g., Nymphaea, Nelumbo, Trapa With erect shoots (amphibious, marshy plants: grow in shallow water along the margin of pond/lake e.g., Ranunculus, Typha, Cyperus
Types of Hydrophytes
What is ecads?
An ecad of a plant species is a population of individuals which although belong to the same genetic stock (genetically similar) but differ in vegetative characters such as size, shape, number of leaves, stem etc.
OR
Genetically similar organisms differing in their phenotype (such size, shape, color etc..) are known as ecads.
Ecophene
In this case- the individuals of a species growing under different environmental conditions differ in external appearance but these changes are only temporary, not permanent, and hence reversible.
When such morphologically different races are brought under similar environmental conditions, the variations within them disappear and their next generations are alike.
Such morphological races of species that exhibit temporary variations in response to different environmental conditions are known as Ecads
Ecads
For example, a species of grass called Euphorbia hirta has two different ecophenes; one that has adapted to grow in grassland, are prostrate and profusely branched,
While the plants of same species growing on the footpaths/dry & hard soils are compact, small leaved and cushioned.
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Euphorbia hirta
Ecotypes
An ecotype is a population of individuals of a species, which are genetically different. Since different ecotypes are inter-fertile, these are kept under the same taxonomic species. Their variations are permanent and irreversible as these are genetically fixed.
Ecotypes
Ecotype: distinct genotypes (or population) within a species, resulting from adaptation to local environmental conditions, capable of interbreeding with other ecotypes of the same species.
Ecotypes arise due to mutations, hybridization and isolation.
Ecotypes
For example, individuals of a species growing at higher altitude may be dwarf or short in height in comparison to growing in plane areas. A number of differences in morphology of a species can be seen in response to different habitat or climatic conditions. Often these variations may become genotypic or inheritable i.e.
transferred from one generation to the other. In other words, these variations become genetically fixed.
Such morphological races where variations in their external appearance are transferred from one generation to other are known as Ecotype
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Ecotypes
Ecotypes thus are those individuals of a species that vary in external appearance and their variations are genetically fixed and irreversible. Other names of ecotypes are ecological races or physiological races.
If such ecotypes are brought under similar environmental conditions, differences between them persist since these are genetically fixed.
Swedish gene ecologist G. Turesson first gave this concept (occurrence of morphological races of a species) in 1922 and 1930.
Ecotypes
Research Note:
Clausen, Keck, and Hiesey (1948) studied the ecotypic races of Achillea lanulosa (yarrow) across the Sierra Nevada. With rising elevation, winter temperature drops below freezing, so that winter dormancy is necessary and plants are smaller. On the eastern slope of the mountains, individuals flower late and are adapted to the cold, arid climate.
The researchers collected seeds from a series of these yarrow populations and raised them in a greenhouse at Stanford University.
Ecotypes
Achillea lanulosa (yarrow)
Ecotypes
Achillea lanulosa (yarrow)
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Representatives of populations of Achillea lanulosa as grown in a uniform garden at Stanford. They originated in the different localities shown in the profile below of a transect across central California at approximately 38 degrees N latitude. Elevations are to the scale shown in meters. Horizontal distances are not to scale.
The plants represent a population of approximately 60 individuals.
The frequency diagrams show variation in height within each population. The specimens represent plants of average height, and the lines above each plant indicate the mean heights.
Ecotypes
Achillea lanulosa (yarrow)
Since the major attributes of these races were maintained when grown under uniform conditions in the same place, it is clear that these adaptations had a genetic basis. That is, each of the races had diverged genetically from the others in response to the challenges of their local environments.
Ecotypes
Achillea lanulosa (yarrow)
Characteristic features of ecotypes
1. Ecotypes of a species, though genotypically distinct, are always inter- fertile.
2. They retain their original features when cultivated in a natural habitat.
3. Variation of ecotypes are genetically fixed.
4. Ecotypes occurs in distinct habitat.
5. Ecotypes are discrete entities with clear differences, which separate one ecotype from another.
6. Differences between ecotypes are actually due to natural selection of locally adapted populations.
Ecoclines
The concept of ecocline (coined independently by Whittaker 1960 and, as coenocline, by van der Maarel
&Westhoff 1964), a gradient zone which is relatively heterogeneous but environmentally more stable.
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dependent of one or two physico-chemical factors of life(say temperature), and thus presence/absence of certain species. It can be understood as "physical transition zone".
“Transition zone based on a single physical factor like heat, salinity, etc. which cause variation in species is ecocline”
Examples : An ecocline can be a THERMOCLINE, chemocline (chemical gradient), halocline (salinity gradient) or pycnocline (variations in density of water induced by temperature or salinity).
Ecoclines
Ecocline
Temperature change and water availability are the most important factors affecting ecocline pattern.
Adaptations in relation to soil oligotrophy
Oligotrophy: Oligotrophs are adapted to exploit ecological niches characterized by low substrate concentrations and low energy flows.
Oligotrophic - poor nutrient
Oligotrophic organisms are those that are adapted to uninterrupted nutrient limitation. Such microorganisms have physiological and morphological characteristics that maximize their ability to import inorganic nutrients or organic substrates across steep gradients (i.e. from very low external concentrations) and utilize these resources conservatively (i.e., usually grow slowly).
Oligotrophic System
ü Water is clear and appears blue to blue green in the sunlight.
ü The nutrient content in the water is low; and also nitrogen in abundant, phosphorus is highly limited.
ü Low production of organic mater, particularly phytoplankton.
ü Oxygen concentration remains high.
ü Free of weeds or large algae blooms.
ü No food for bacteria.
ü Sandy, rocky bottom.
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Crater Lake, Oregon (USA): 2nd deepest in World. Hemisphere (589 m); ultra-oligotrophic
Winter
Summer
Oligotrophic System
The ecological significance of oligotrophs is that they not only grow at low nutrient concentrations, but their activities are also responsible for reducing concentrations of low-molecular weight carbon compounds below threshold levels for catabolite repression for hydrolysis, so that production of enzymes can take place that are repressed by high catabolite concentrations.
Oligotrophic System
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