Lecture 4- Adaptations of sclerophyll plants

Question 1

What is a xeromorph?

Answer 1

-a plant that has a form (morph) that enables it to live in dry and stressed environments

Question 2

Why were/are xeromorphs favoured in the Australian climate?

Answer 2

-increased aridity, increased fire frequency and weathering soils during the last 30 MY favoured the evolution and dominance of xeromorphs

Question 3

What are the two types of xeromorphs?

Answer 3

1. succulents

2. sclerophylls

Question 4

What are the characteristics of succulent plants?

Answer 4

• 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

Question 5

Where are chenopod shrublands common?

Answer 5

• in deserts of Australia

- succulent plants

Question 6

What are the adaptations of succulents?

Answer 6

• 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

Question 7

What are the sclerophylls?

Answer 7

• more common than succulents
• tough rigid leaves that do not wilt when water stressed
• e.g. Family Protaceae Banksia

Question 8

What are the adaptations of sclerophylls?

Answer 8

1. often small leaf size
2. short internodes
3. proportionally thick leaves
4. reduced surface area/volume ratio

Question 9

What are the anatomical features of sclerophylls?

Answer 9

• 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

Question 10

What is special about desert grasses?

Answer 10

-leaf rolling to reduce water loss

Question 11

Why did sclerophylly first evolve?

Answer 11

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)

Question 12

Why might sclerophylly be an adaptation to low nutrient soils?

Answer 12

• 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

Question 13

Why might sclerophylly have first evolved in response to low nutrient soils?

Answer 13

• 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

Question 14

What are many sclerophylls adapted to survive?

Answer 14

-fire

Question 15

What do the effects of fire depend on?

Answer 15

-temperature and duration (speed) of fire: very fast hot fire may do less damage than a slow long fire

Question 16

What are the sclerophyll adaptations to fire? (3)

Answer 16

1. Tolerance of fire: protective features, even stimulate by fire to flower
2. Adult plant killed but seeds survive
3. Plants promote fire e.g. eucalyptus with oil in leaves help fire to burn rapidly (less damage)

Question 17

What are the types of strategies for surviving fires (sclerophylls)?

Answer 17

1. Re-sprouting

2. Seeding a) canopy seed bank or b) soil seed bank

Question 18

How do plants protect themselves against fire with bark?

Answer 18

• 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

Question 19

What are the types of sprouting (budding) after a fire? (vegetative reproduction after a fire)

Answer 19

1. Dormant buds: aerial: epicormic

2. Underground buds: lignotubers, rhizomes, root suckers

Question 20

What is aerial sprouting/budding?

Answer 20

• 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

Question 21

What are the underground buds in plants? (examples)

Answer 21

• 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)

Question 22

What is regeneration from seed after fire like? (canopy seed bank)

Answer 22

• 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

Question 23

What is the soils seed bank system like?

Answer 23

-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=

Question 24

What is myrmecochory?

Answer 24

• 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