Lecture 5: Adaptions to light Flashcards
light powers tropical forests via
photosynthesis
the ability to exploit such contrasting habitats is possible because plants have evolved
various mechanisms to optimise their use of sunlight and survive in deep shade
–they also have the ability to acclimate to changes in irradiance
acclimation :
the process of adapting to a new environment
many plants exhibit great ___ in their response to changes in light availability within a particular habitat
plasticity
the potential for acclimation to changes in irradiance enables plants to
exploit more variable environment than plants with a narrower range of responses to light
sunflecks:
plants on the forest floor are exposed to short bursts of irradiance
sun flecks: plants adaption
sun flecks are dynamic can vary in freq and intensity - plants need to be adapted to use this energy when available
sun flecks are a major source of
energy for maintanenece and for growth in the undersotrey
sun flecks can contribute ___% of the total daily light exposure and can enhance C gain by ___% for understory plants
- 10-85%
- 60-70%
changes in irradiance during the life of a tree:
- 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
adaption of Begonia erythrophylla to maximise light interception in the understory
- 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.
adaptions of understory plants to maximise light interception:
- anthocyanins
- blue iridescence
anthocyanins:
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
blue iridescence
- 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
tree form and leaf placement affect the efficient of
light capture
tree form and leaf placement affect the efficient of light capture: understorey trees:
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.
tree form and leaf placement affect the efficient of light capture: trees in sun
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)
can trees exhibit changes in form and leaf angle at different stages of their lifecycle?
YES
shade tolerant trees need to maximise irradiance as they grow beneath a canopy but their crowns will…
eventually emerge into full sunlight
light compensation point is higher in sun/shade plants?
SUN is higher
sun vs shade: CELLS SUN
SUN:
- large cells
- small chloroplasts
- low chlorophyll/Rubsico ratio
- high chlorophyll a/b ratio
- high N content
- high xanthophyll cycle pigments
sun vs shade: CELLS SHADE
- small cells
- large chloroplasts
- high chlorophyll/Rubisco ratio
- low chlorophyll a/b ratio
- low N content
- low xanthophyll cycle pigments
sun leaves are more
rigid as this reduces wilting and susceptibility to drought
sun leaves often contain large amount of ____ ___ pigments which ______
carotenoid xanthophyll pigments which protect against damage from excess irradiance
