Lecture 5: Adaptions to light

Question 1

light powers tropical forests via

Answer 1

photosynthesis

Question 2

the ability to exploit such contrasting habitats is possible because plants have evolved

Answer 2

various mechanisms to optimise their use of sunlight and survive in deep shade
–they also have the ability to acclimate to changes in irradiance

Question 3

acclimation :

Answer 3

the process of adapting to a new environment

Question 4

many plants exhibit great ___ in their response to changes in light availability within a particular habitat

Answer 4

plasticity

Question 5

the potential for acclimation to changes in irradiance enables plants to

Answer 5

exploit more variable environment than plants with a narrower range of responses to light

Question 6

sunflecks:

Answer 6

plants on the forest floor are exposed to short bursts of irradiance

Question 7

sun flecks: plants adaption

Answer 7

sun flecks are dynamic can vary in freq and intensity - plants need to be adapted to use this energy when available

Question 8

sun flecks are a major source of

Answer 8

energy for maintanenece and for growth in the undersotrey

Question 9

sun flecks can contribute ___% of the total daily light exposure and can enhance C gain by ___% for understory plants

Answer 9

• 10-85%

- 60-70%

Question 10

changes in irradiance during the life of a tree:

Answer 10

• climax trees start life in understory and following the opening of a gap irradiance will increase
• seedlings need to be able to adapt and take adv
• Plasticity and the ability to acclimate to both short and longer term changes in irradiance are important determinants of the ability to compete, establish and survive

Question 11

adaption of Begonia erythrophylla to maximise light interception in the understory

Answer 11

• B. erythrophylla has evolved epidermal cells that behave like lenses that focus light onto the chloroplasts.
• The irradiance reaching the chloroplasts is 15 time greater than the incident light at the surface of the leaf.

Question 12

adaptions of understory plants to maximise light interception:

Answer 12

• anthocyanins

- blue iridescence

Question 13

anthocyanins:

Answer 13

some monocots and dicots posses red or purple anthocyanin pigments on the underside of leaves which increases the efficiency of light capture by reflecting back absorbed light into the leaf

Question 14

blue iridescence

Answer 14

• A few species of plants in the taxa Selaginella, Melastomataceae and Begoniaceae posses blue iridescence.
• This result from microscopic anatomical features that interfere with light and increase capture of photosynthetically active radiation at the red end of the spectrum

Question 15

tree form and leaf placement affect the efficient of

Answer 15

light capture

Question 16

tree form and leaf placement affect the efficient of light capture: understorey trees:

Answer 16

Understorey trees often possess horizontally inclined branches (plagiotropic) with fairly large well spaced leaves. Self-shading can be minimised by leaf shape size and angle.

Question 17

tree form and leaf placement affect the efficient of light capture: trees in sun

Answer 17

Trees growing in sun tend to have more vertical growth (orthotropic) with small leaves that tend to be oriented further from the horizontal to avoid damage from excess irradiance (photoinhibition)

Question 18

can trees exhibit changes in form and leaf angle at different stages of their lifecycle?

Answer 18

YES

Question 19

shade tolerant trees need to maximise irradiance as they grow beneath a canopy but their crowns will…

Answer 19

eventually emerge into full sunlight

Question 20

light compensation point is higher in sun/shade plants?

Answer 20

SUN is higher

Question 21

sun vs shade: CELLS SUN

Answer 21

SUN:

• large cells
• small chloroplasts
• low chlorophyll/Rubsico ratio
• high chlorophyll a/b ratio
• high N content
• high xanthophyll cycle pigments

Question 22

sun vs shade: CELLS SHADE

Answer 22

• small cells
• large chloroplasts
• high chlorophyll/Rubisco ratio
• low chlorophyll a/b ratio
• low N content
• low xanthophyll cycle pigments

Question 23

sun leaves are more

Answer 23

rigid as this reduces wilting and susceptibility to drought

Question 24

sun leaves often contain large amount of ____ ___ pigments which ______

Answer 24

carotenoid xanthophyll pigments which protect against damage from excess irradiance