Lecture Eleven - Plant adaptations Flashcards
What are the four basic functions plants must maintain?
Water uptake.
Nutrient uptake.
Photosynthesis.
What are biological constraints?
Biological constraints are physical or biological processes that limit the phenotype possible for evolution.
Organisms must obey the laws of chemistry and physics.
- Biomechanics.
- Thermodynamics.
Trade offs amount functions:
- Allocation of energy.
- Zero sun dynamics (energy in = energy out).
What wave lengths do plants and algal cells use?
Between 400 and 790 nm (Photosynthetically Active Radiation or PAR).
What are the three general classes of adaptations in plants?
Behavioral, physiological and structural adaptations.
What are adaptations to improve plants performance in low light?
More chlorophyll.
Increased stacking of grabs thylakoids.
Thinner leaves.
Sun and shade adapted plants can be distinguished by their photosynthetic and photo flux responses.
Sub plants have greater photosynthetic capacity, but shaded leaves perform better at low light.
What are thee ways for a plant to get to the canopy?
Grow from ground and support yourself (trees).
Grow from ground and be supported by someone else (lianas).
Grow from within crown of tree (epiphytes and hemi-epiphytes).
What are hemi-epiphytes?
Establish in crowns of other tree.
Water and nitrate storage in tuberous aerial roots.
May not reproduce until roots have reached the ground.
Eventually kill host and support themselves.
How can plants cope with too much light?
Too much light can cause photo inhibition and photo oxidative damage.
Adaptations to minimize high light stress:
Reflective leaf surface.
- Hairy leaves (increases scattering).
- Shiny leaves (increased reflective ability).
Biochemical mechanisms to prevent photo oxidation.
Adjust leaf angle relative to incoming sun.
How much water is lost per gram of C assimilated?
For every gram if carbon assimilated into plant matter, 400-500g of water is lost from the plant via transpiration.
What are plant responses to water stress?
Behavioral:
Avoid the problem.
- Only grow when water is available (ephemeral/opportunistic species).
- Only grow where water is always available (habitat specialist).
Tolerate the problem.
- Seed heteroblasty -> variability in timing of germination.
- Drop leaves during dry periods.
- Deeper, larger roots.
Physiological:
In mesophytes (require conditions that are not too wet nor too dry) water loss is controlled by closure of stomata.
As water is lost from the plant, changed in turgor stimulate production of abscission acid, causing stomatal closure.
Three photosynthetic pathways - C3, C4 and CAM.
CAM = Common in succulents, stomata open at night and store CO2. Stored CO2 is used during the day for photosynthesis.
Structural:
Plants can lose water through the leaf surface if diffusion gradient is strong enough.
Xerophytes have anatomical (and physiological) adaptations that allow then to survive when little water is available.
- Waxy leaf surface = thick cuticle prevents water loss from epidermal cells.
- Hairs = increased a boundary layer of still air over leaf surface.
- Sunken stomata = air directly above stone is still (often protected by hairs).
- Leaf rolling = surrounds one leaf surface with a layer of still air.
How is water acquired in plants?
Enhanced root systems:
Deep tap roots to exploit water table.
Wide spread shallow roots to take advantage if small rain fall events.
Swollen stem and trunks:
Store water in stems and trunks for use when soil water supply is depleted.
What are plant adaptations to nutrient uptake?
Critical because more physiological activities requires nutrients.
Australian soils are typically nutrient poor.
Strategies to increase nutrient acquisition.
- Root structure.
Root hairs increase the surface are for absorption of nutrients.
- Symbiotic association.
Bacteria fix nitrogen from the atmosphere and pass on fixed nitrogen to the plant in return for carbohydrates.
Ecto- and endo-mycorrhizae fungi allow plant root systems to exploit more soil. Ecto-mycorrhizae form a net or sheath around the roots without entering the plant cells.
Endo-mycorrhizae actually penetrate the plant cells.
In arbuscular mycorrhizae the fungus forms highly branched structures called arbuscules within the plant cells to aid exchange of materials between the plant and fungus.
- Carnivore.
If soil nutrients are limits g, carnivory can make significant contributions to plant nutrition and growth.
Nell xx
