Lecture 4- Adaptations of sclerophyll plants Flashcards
What is a xeromorph?
-a plant that has a form (morph) that enables it to live in dry and stressed environments
Why were/are xeromorphs favoured in the Australian climate?
-increased aridity, increased fire frequency and weathering soils during the last 30 MY favoured the evolution and dominance of xeromorphs
What are the two types of xeromorphs?
- succulents
2. sclerophylls
What are the characteristics of succulent plants?
- plants fleshy, with cells large and filled with watery sap
- drought and salt tolerant
- often reduced leaves
- stem photosynthetic
- not as common
- family: Chenopodiaceae (saltbushes) of deserts; related to coastal saltmarsh plants
Where are chenopod shrublands common?
- in deserts of Australia
- succulent plants
What are the adaptations of succulents?
- light-coloured= surface colour reflects radiation
- covered with bladder cells into which the leaves actively pump salt so it cannot harm the plant and eventually the leaves fall off
What are the sclerophylls?
- more common than succulents
- tough rigid leaves that do not wilt when water stressed
- e.g. Family Protaceae Banksia
What are the adaptations of sclerophylls?
- often small leaf size
- short internodes
- proportionally thick leaves
- reduced surface area/volume ratio
What are the anatomical features of sclerophylls?
- thick-walled cells (sclerids, fibres)
- lignin in walls
- thick cuticle and waxy coating
- sunken stomata
- leaf hairs reduce evapotranspiration: boundary layer
- leaf rolling in grasses
What is special about desert grasses?
-leaf rolling to reduce water loss
Why did sclerophylly first evolve?
Beadle’s hypothesis: sclerophylly first evolved on soils of low nutrient level, especially phosphorus
- the soil under rainforest: phosphorus high 500-2500ppm
- the soil under sclerophylls: phosphorus low (Eucalyptus 160-320ppm, Banksia 130-400ppm)
Why might sclerophylly be an adaptation to low nutrient soils?
- lack of nutrients can limit plant cell growth and metabolism e.g. P is critically important as backbone of nucleic acids, in ATP, cell membranes etc.
- slow growth, smaller leaves and internodes, carbohydrates channeled into lignin, thick cell walls= more efficient use of nutrients
Why might sclerophylly have first evolved in response to low nutrient soils?
- Sclerophyllous plants evident before the onset of aridity in Australia e.g. fossil Banksia 50 MYA
- hypothesis: slow growth, small cells, carbohydrates channeled into lignin, thick cell walls, which pre-adapted plants to increased aridity
- so they existed on the soils that were less fertile
- in time when australia was moist
What are many sclerophylls adapted to survive?
-fire
What do the effects of fire depend on?
-temperature and duration (speed) of fire: very fast hot fire may do less damage than a slow long fire
What are the sclerophyll adaptations to fire? (3)
- Tolerance of fire: protective features, even stimulate by fire to flower
- Adult plant killed but seeds survive
- Plants promote fire e.g. eucalyptus with oil in leaves help fire to burn rapidly (less damage)
What are the types of strategies for surviving fires (sclerophylls)?
- Re-sprouting
2. Seeding a) canopy seed bank or b) soil seed bank
How do plants protect themselves against fire with bark?
- thick fibrous outer bark (corky layers) protects living parts= phloem and cambium
- protects the living tissue underneath, prevents the inner tissue getting too hot
- phloem= allows carbohydrate transport
- can easily kill a plant by taking a section of the bark and phloem around= severe the connection from canopy to roots= will die
What are the types of sprouting (budding) after a fire? (vegetative reproduction after a fire)
- Dormant buds: aerial: epicormic
2. Underground buds: lignotubers, rhizomes, root suckers
What is aerial sprouting/budding?
- dormant buds under the bark, can sprout after fire so has new leaves to sustain it
- eventually new branches will grow and canopy will reform, connected to competition
What are the underground buds in plants? (examples)
- lignotubers:eucalypts= multistem eucalypts,large woody swelling= lignotuber= rich in carbs etc, and has lot of buds, so if destroyed by fire puts out new branch
- rhizome (bracken)= underground and protected from fire so can put out new shoots after a fire, often the first organisms that come up after a fire
- root suckers (Acacia)
What is regeneration from seed after fire like? (canopy seed bank)
- seeds released from woody fruits
- -preservation of seeds even if the adult plant dies in the fire
- some the banksias will not open unless they go through fire
What is the soils seed bank system like?
-seeds with hard coats, cracked by heat, imbibe water and germinate (peas and acacias)
soil seed bank= store of seeds underground
-the seeds fall to the ground over years and don’t germinate until a fire occurs, this is so the plant doesn’t die out because of the fire
-cracks due to heat, then rain and germination is possible then
= this is about acacias
-flat part of the seed= the funicle functions as an elaiosome=
What is myrmecochory?
- seed dispersal by ants
- common in Australia (c. 87 genera, 24 families)
- ants harvest seed, bury underground, discard hard seed and eat reward, both species benefit
