L5 Adaptations to light in tropical rainforests

Question 1

Why is light important in a tropical forest?

Answer 1

Powers the forest via photosynthesis, is the dominating factor in rainforest growth

Question 2

What is plasticity?

Answer 2

The ability to acclimate to changing conditions

Question 3

What is acclimation?

Answer 3

The process of an individual adapting to a new environment

Question 4

What does having a high potential for acclimation mean for plants?

Answer 4

Able to exploit more environments that plants with a narrow tolerance range

Question 5

What is an example of rapid changes in irradiance on the forest floor?

Answer 5

Sunflecks

Question 6

Why are sun flecks so important for rainforest ecology?

Answer 6

are a major source of energy for the maintain and growth of the understory: 10 - 85% of the totally daily light exposure

Question 7

When are long term changes in irradiance experienced?

Answer 7

For climax seedlings, over its lifetime, as it grows out of the understory into the emergent canopy, going from shade to full sunlight

Question 8

What are shade requiring plants?

Answer 8

Cant begin to grow until in the shade

Question 9

What differences do are seen in leaves at the top and bottom of the trees?

Answer 9

Different physiology to cope with different exposure to irradiance

Question 10

What adaptation is see by Begonia erythrophylla to maximise light in the understory?

Answer 10

evolved epidermal cells that behave like lenses that focus light onto the chloroplasts, 15 times the amount of irradiance reaches focus points than normal

Question 11

Why do the leaves of some plants in the understory appear blue?

Answer 11

Some leaves may appear iridescent blue, due to microscopic anatomical features that interfere with light to increase capture of photosynthetically active radiation at the red end of the spectrum - irradiance appears as light is scattered

Question 12

How do anthocyanins increase light capture in the understory?

Answer 12

red or purple anthocyanin pigments on the underside of the leaf increases the efficiency of light capture by reflecting back absorbed light into the leaf

Question 13

What form of understory trees normally take?

Answer 13

Horizontally grown branches, plagiotrophic, with large and well spaced leaves to minimise self shading

Question 14

What form do trees in full sun take?

Answer 14

Vertically grown branches, orthotrophic, with small leaves that tend to be oriented further from the horizontal to reduce damage from excess irradiance

Question 15

What specialisation is seen by the pioneer tree Macaranga gigantia?

Answer 15

Produces large leaves near to the stem, expansion take three weeks, but the stem continues to extend for 91 days, which allows the ageing leaf to extend beyond the newly produced leaves further down, to avoid shading them

Question 16

Why are there differences between plant growing in the sun and the shade?

Answer 16

because leaves growing in the shade need to be adapted to maximise light capture, even for shade requirement. Plant in the sun need to be able to deal with excess irradiance

Question 17

What are the characteristics of the cells of sun plants?

Answer 17

large cells
small chloroplasts
Low chlorophyll/Rubisco rate 
High chlorophyll a/b ratio
High N content 
High xanthophyll cycle pigments

Question 18

What are the characteristics of the cells of shade plants?

Answer 18

Small cells
large chloroplasts
High chlorophyll/Rubisco rate 
Low chlorophyll a/b ratio
Low N content 
Low xanthophyll cycle pigments

Question 19

What are the characteristics of the leaves of sun plants?

Answer 19

Small thick leaves, 
High stomatal density 
High rate of respiration 
High chlorophyll a/b ratio
Low specific leaf area per unit mass
High N content 
High xanthophyll cycle pigments

Question 20

What are the characteristics of the leaves of shade plants?

Answer 20

Large thin leaves 
Small stomatal density 
Low transpiration rate
Low chlorophyll a/b ratio
High specific leaf area per unit mass
Low N content 
Low xanthophyll cycle pigments

Question 21

What are the main characteristics of sun plants?

Answer 21

Vertical leaf orientation 
High leaf area index
more canopy layers 
Shorter leaf lifespan, high turnover 
Leaves rigid

Question 22

What are the main characteristics of shade plants?

Answer 22

Horizontal leaf orientation
Low leaf area index
Less canopy layers
Longer leaf lifespan, low turnover

Question 23

What are the growing requirements of the S .leprosula?

Answer 23

Climax species, requires higher light, seedlings don’t survive long in deep shade

Question 24

What are the growing requirements of the D.lancelolata?

Answer 24

Seedlings survive in a wide range of light conditions, form deep shade to large canopy gap

Question 25

What was the aim of the experiment carried out of s.leprosula and d.lacelolata in danum valley?

Answer 25

To determine if interspecific differences in the seedling ecology of two climax dipterocarp trees reflected differences in the ability to acclimate to different light environments

Question 26

What are the three environments the s.leprosula and d.lacelolata saplings were planted in?

Answer 26

Undisturbed primary rainforest
5 year old secondary forest understory
1 year old secondary forest understory