BIOL 1262 - (BOTANY) Adaptations Of Plants To Extreme Habitats

What are the suitable conditions and adaptations for varying extreme habitats' environments?

(1) Dry environment - very dry conditions, Xerophytes adaptation (2) Aquatic - marine and freshwater, Hydrophytes adaptation (3) Low light - Tropical RainForest (TRF) understory / floor, Epiphytes adaptation (4) Low soil nitrogen - Little or no nitrogen in the soil, Carnivorous adaptation (5) Mangrove ecosystems - High salt content, Halophytes

Leaf reflectance/absorbance

(1) Leaves with shiny surfaces - have shiny thick waxy cuticle that reflects light and reduce evaporation and heat buildup. (2) Leaves with whitish surfaces - Many epidermal trichomes make the leaves appear white and reduce heating effect of photosynthetic active radiation (PAR), leaf temperature, transpiration rates and heat buildup.

Extreme habitat conditions are determined principally by two abiotic factors. What are they?

(1) Physical extremes - temperature, radiation, pressure (2) Geothermal extremes - desiccation, salinity, pH, oxygen species

List 3 halophyte mechanisms found in many species of mangrove.

(1) Salinity avoiders (2) Salinity evaders (3) Salt tolerant plants (euhalophytes)

List the xerophytic adaptions.

(1) Seasonal dormancy*seeds remain dormant until the brief rainy period* /deciduousness (2) Microphylly - small leaves are less likely to become heated. There are more spaces between the leaflets for circulation of air. (3) Helionastic responses - responses to the sun so they move in relation to the sun e.g. sunflowers always faces the sun (4) Reflectance - plants reflect sunlight and radiation reducing the heating effect of sunlight (5) Hairy leaves - white hairy leaves reflect light so less heat on the plant (6) Sunken stomata (Stomata in pits with hairs) - result in diffusion wells, stomata in depressions with humidity which will reduce the evaporation of water from the stomata (7) Leaf folding - most of stomata are on one surface of the leaves, the stomata are in a common area that is humid and so evaporation is reduced (8) Leaf rolling (same information as leaf folding) (9) CAM metabolism - Crassulacean acid metabolism (plants close stomata in the day to protect the plant from losing water, take in CO2 and O2 in the night and night transpiration) (10) Thicker waxy cuticle - Reduce water loss (11) Lower growth to ground - further away from the sun

What are the four types of entrapment of Carnivorous plants?

(1) Sticky hairs (2) Bladders with partial vacuum (3) Drown (4) Spring trap

What crucial factors determine the distribution of plants and animals over the surface of the globe?

(1) Water supply (2) Environmental temperature (3) Gaseous exchange (4) Seasonal Variation

What makes a habitat ideal for plants?

(1) supplies resources in sufficient quantities for growth and reproduction. e.g. light, water, nutrients (2) provides pollinators, dispersers and other symbionts (3) has few herbivores, predators and parasites except those that afflict their competitors.

What are the characteristics of succulent xerophyte plants?

1) Absorb and retain moisture in adapted thick, fleshy portions of the plant 2) Store water in their stems or leaves • Spines to discourage animals from eating plants for water 3) Often contain mucilage which helps with water storage - Mucilage holds on to the water so it does not evaporate as easily, it is not as available as evaporation or transpiration as just regular water would be 4) Have very low surface area : volume ratio 5) Low transpiration rate i.e. less cuticle 6) Slower growing so require less energy. • The plants don't have to make as much food and therefore do not lose as much water

Because halophytes habitats are physiologically equivalent to dry habitats they develop xerophytic features. What are they?

1. Presence of thick cuticle on the aerial parts 2. Leaves may be dorsiventral (dicot) or isobilateral (monocot) with protected stomata 3. Mucilage cells may be found in abundance 4. Pubescence - covered with various types of simple and branched trichomes: a. greyish appearance - reflect heat b. improved water economy, c. preventing temperature build-up in leaves d. preventing sea water droplets from reaching the internal tissues of the leaves 5. Altered flowering schedule 6. Sequestration of ions in vacuoles 7. Partitioning of toxic ions to leaves 8. Excretion of salt through salt glands 9. Restricting entry of ions at roots

What are the two major types of xerophytes?

1. Succulent xerophytes: Absorb and retain moisture in adapted thick, fleshy portions of the plant 2. Non-succulent xerophytes: Tough, dry plants

Physical Extremes

1. Temperature - creates a series of challenges, from the structural devastation wrought by ice crystals at one extreme (when it's too cold), to the denaturation of biomolecules (such as enzymes) at the other (when it's too hot) 2. Radiation (light energy) - can inhibit photosynthesis but the more serious damage is to nucleic acids causing mutations. 3. Pressure - challenges life because it forces volume changes, hence changes in form. Pressure compresses packing of lipids resulting in decreased membrane fluidity

List the characteristics of non-succulent plants.

1. Tough, dry plants 2. High proportion of fibre (non-living material) 3. Restrict their growth activity to periods when moisture is available 4. Drought-deciduous which are dormant or die back during dry periods 5. Drop their leaves, and sometimes their stems during periods of drought 6. Some are aphyllous • without leaves, relying on stem photosynthesis 7. Adapted leaves with stiff texture - have large amounts of sclerenchyma tissue 8. Adapted stems: leaves are extremely reduced, highly branched and photosynthetic

Geochemical extremes

1. desiccation (state of extreme dryness) - Water possesses many properties that seem to make it the essential solvent for life 2. salinity - Organisms live within a range of salinities, from essentially distilled water to saturated salt solutions 3. pH - Biological processes (are affected largely through the enzymes which control them) tend to occur towards the middle range of the pH spectrum 4. oxygen species (oxygen supply) - organisms inhabit environments ranging from strictly anaerobic to aerobic (aerobic have reactive oxygen species which happen which are mostly free radicals which form due to the presence of oxygen).

Use diffusion shells to explain why plants transpire faster on a windy day than on a still one.

1. thick boundary layer of diffusion shells (unstirred air [transpired water vapour] close to the leaf), gentle (water potential) gradient, slow diffusion 2. thin boundary layer, steep gradient, fast diffusion When wind stirs up the air close to the leave it makes the boundary layer thinner which makes plants transpire faster on a windy day than on a still one. In moving air water vapour is removed from the leaf's surface so the water potential gradient is increased; water potential gradient moves from a higher (less negative) to a lower (more negative) water potential gradient so faster rate of water evaporation via the stomata.

What are Carnivorous plants aka. insectivorous plants?

Any plant especially adapted for capturing and digesting insects and other animals by means of entrapment and digesting them. They grow in soils in low-nitrogen areas.

Unanchored/ Floating hydrophytes

Are in contact with both air and water but not in soil. e.g. Water hyacinth - Eichhornia sp. (1) Stem soft and spongy due to presence of aerenchyma tissue (large air-filled spaces) for buoyancy and air storage (2) Much reduced root system (3) Some have hairs on leaves to prevent water lodging and obstructing gaseous exchange e.g. Salvinia sp. (fern)

Define extreme habitat. Give examples.

Areas with characteristics that lie outside of the normal range of conditions in which organisms would be expected to live. e.g. tundra, deserts, ecotones

Specialized metabolism: C3, C4 and CAM photosynthesis

C3 - takes place in mesophyll cells, advantage: energy efficient, disadvantage: water loss due to evaporation in warm weather, pathway: CO2 --> Rubisco --> G3P--> sugar C4 - take place in mesophyll cells and bundle sheath, advantage: water loss is minimized in warm weather, disadvantage: requires more energy, pathway: malic acid -->CO2 --> Rubisco --> G3P --> sugar CAM - takes place in mesophyll cells : water loss is minimized in hot weather, disadvantages: requires more energy, slower growth, pathway: malic acid -->CO2 --> Rubisco --> G3P --> sugar

What are Halophytes?

Flora of saline environments; Plants that complete their life cycle in habitats with an appreciable salt content (saline habitats). Many halophytes grow in areas that are not only saline but are also prone to standing salt water • e.g. mangroves

Spring trap

Hinged leaf with sensitive trigger hairs

Drown

Insect drowns in water e.g. Pitcher plants

Bladders with partial vacuum

Insect sucked into bladder e.g. Bladderworts Inside of the bladder there is a partial vacuum. When an insect passes the trigger hairs it causes the bladder door to open, sucking the insect inside and closes the door again with the insect trapped inside it underwater.

Sticky hairs

Insect trapped on hairs e.g. sundew plants

Helionasty aka. *heliotropism

Involves the reorientation of leaves by a pulvinus. Pulvinus is the base of each leaflet, it contains cells which are filled with water that applies pressure against the cell wall called turgor pressure which helps the leaves stand upright. When the leaflet is touched or very hard wind is blown on it, specific parts of the plant release certain chemicals so that water is loss by the cells in the plant's pulvinus, turgor pressure is then gone resulting in the cells collapsing and the leaflets closes up. - Leaves of many well-watered plants remain perpendicular to the sun's rays. - the directional growth of a plant in response to sunlight *Sunflowers face the sun at all hours during the day.

CAM Metabolism - Crassulacean Acid Metabolism

Light Independent RXN common in many desert plants. Plants such as many cacti close their stomata in daytime. Open them in the cool nights, fix CO2 to malic acid. This adaptation reduces evapotranspiration and increases efficiency in the use of water.

What's the relation to stomata and leaf shape direction to the sun?

Most leaves will have more stomata on lower epidermis than upper epidermis and those are the plants that have their leaves horizontal i.e. the light strikes them at 90 degree angle, plants whose leaves are oblique (neither parallel nor at right angles) to the sun have equal amount of stomata on both upper and lower epidermis.

Drought-deciduous Xerophytes

Plants do not resist water loss in dry weather. They dry up and become dormant, but remain alive. In damp weather, they absorb water and resume activity.

What are hydrophytes?

Plants that are adapted to living in water or very wet habitats.

Non-heliotropic plants

Plants which are not heliotropic often have more vertical leaves at the top of the plant while the lower leaves are more horizontal and this is largely because the younger leaves at the top have cuticle that needs to be further developed those leaves further down are more mature and so they are able to withstand full brunt (the worst part or chief impact of a specified action) in perpendicular to the sunrays being more horizontal.

What are xerophytes?

Plants which grow in very dry environments or prolonged drought.

What are Epiphytes?

Plants which survive in areas of low light intensity by growing on other plants or objects (such as telephone and electricity lines) ONLY for physical support and to gain access to light. E.g. Grape (Vitis vinifera) Cho-cho (Sedium edule), Old man's beard / ball moss (Tillandsia usneoides) a bromeliad *Features: - Depend on rain water / dew and dust to provide moisture and nutrients respectively - Able to colonize quickly by having clasping roots. e.g. orchids

Describe the habitats of halophytes.

The habitat is wet but it is equivalent physiologically to a dry habitat. • Ecotone between marine and terrestrial biomes • Salt spray - a significant source of salt in coastal areas from the breaking waves blown by onshore winds • Marine submerged and exposed areas • Terrestrial desert areas • Soils damaged by the abuse of artificial fertilizers

What is a habitat?

The natural habitat in which an organism characteristically lives and is ideal.

Salt tolerant plants (euhalophytes)

The protoplasm of their cells endures a high salt concentration

Dionaea Leaf trap mechanism

The trigger hairs are stimulated by the pressure of an insect brushing by the hairs. Mechanical energy is converted to electrical energy so the electrical impulses travel quickly across the lamina to the central midrib. These electrical impulses open up specialized pores in the cells of the midrib. Water then is quickly transferred out of the upper cells thus loss of turgor in the upper epidermis which results in the 'trap' to shut enclosing the insect. This mechanism is time elapsed for 10 seconds or less.

Leaf rolling

The upper epidermis has all the stomata and rolls covering all the stomata in humid air, retaining the most air over the surface of the stomata, minimising transpiration. The hinge cells, when flaccid cause the leaf to be rolled up, thus the more flaccid the leaf, the more tightly rolled it becomes shutting stomata from outside atmosphere.

How many MAIN types of hydrophytes exist and what are they?

There are 2 main hydrophytes and they are: (1) Floating hydrophytes (unanchored) (2) Submerged hydrophytes (anchored)

Anchored/submerged hydrophytes

They can either be: (1) Plants in contact with soil, water and air e.g. Pond lily - Nymphaea sp. * feature: water-repellent cuticle - water drops roll off and not block stomata (2) roots in the soil but are not in contact with air; they are fully submerged in water (they are underwater) e.g. turtle grass - Thalassia testudinum (sea grass) *features: 1. rhizomes - anchor the plant to the sandy substratum 2. thin leaves with no cuticle - absorbs nutrients, water, carbon dioxide, light

Why is water supply the most important crucial factor in determining the distribution of plants over the surface of the globe?

Water supply is needed for: (1) cell metabolism - no growth without liquid water (2) transport - transport of minerals (roots to shoots) and fixed carbon (shoots to roots) is facilitated by the bulk flow of liquid water.

Salinity avoiders

a. Accomplish their life cycle within specific seasons of the year • flower at specific times (e.g. rainy seasons) to minimise salt exposure b. Terrestrial halophytes extend their roots down into nonsaline layers of the soil c. Limiting salt uptake - suberized roots

Salinity evaders

a. Accumulating salts in certain cells • compartmentalize ions within vacuoles • accumulation in senescent leaves → leaf abscission b. By actively secreting excess salts • epidermal salt glands, salt-secreting hairs c. Roots that filter seawater