Lecture 4 - adaptations to light in tropical rain forests Flashcards
how have plants adapted to optimise their use of sunlight?
they have the ability to acclimate to changes in irradiance
what is acclimation?
the process of adapting to a new environment
what does the potential of acclimation to changes in irradiance enable plants to do?
they can exploit more variable environments than plants with a narrower range of responses to light
what are sunflecks?
rapid changes in irradiance - plants exposed to short bursts of sunlight
what is the impact of sunflecks?
the dynamic irradiance can vary in frequency and intensity and plants can adapt to use this energy when available - they provide a major source of energy for maintenance and growth in the understorey
what contribution do sunflecks have?
contribute 10-85% of the total daily light exposure and can enhance C gain by 60-70% for understorey plants
why is the ability to acclimate to longer term changes in irradiance also important?
important for climax and shade tolerant species which start life in low sunlight and then need to adapt to the change in sunlight as they emerge from the canopy into full sunlight - this ability of acclimation is important to compete, establish and survive
describe begonia erythrphyllas adaptation
- evolved epidermal cells that behave like lenses that focus light onto the chloroplasts - 15 times greater irradiance - maximises light interception in the understorey
what are the benefit of anthocyanins?
some monocots and dicots possess 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
what is blue iridescence?
- a result from microscopic anatomical features that interfere with light and increase capture of photosynthetically active radiation at the red end of the spectrum
what taxa is blue iridescence seen in?
seliginella
melastomatacae
begoniaceae
what does plagiotropic mean?
horizontal branches
what does orthotropic mean
more vertical growth of branches
describe understorey trees
plagiotropic with fairly large well spaced leaves - self shading can be minimised by leaf shape and size
describe trees in the sun
orthotropic with small leaves orientated further from the horizontal to avoid damage from excess irradiance (photoinhibition)
how can trees adapt to changes in irradiance
trees can exhibit changes in form and leaf angle at different stages of their lifecycle
describe the pioneer tree macaranga gigantia
- produces large leaves near the stem
- expansion takes 3 weeks but petioles continue to extend for 91 days which allows the ageing leaf to extend beyond newly produced leaves just avoiding shading them
describe the differences in leaves/ plants growing in the sun and shade
- anatomically and metabolically different
- quantum yield is the same in both sun and shade plants although the light compensation point is higher in the sun plant
- sun plants achieve a higher rate of light-saturated photosynthesis than shade plants
describe the cells of sun plants
- large cells
- small chloroplasts
- low chlorophyll/rubisco ratio
- high chlorophyll a/b ratio
- high N content
- high xanthophyll cycle pigments to protect against damage
cells of shade plants
- small cells
- large chloroplasts
- high chlorophyll/rubisco ratio
- low chlorophyll a/b ratio
- low N content
- low xanthophyll cycle pigments
leaves of sun plants
- small and thick
- high stomatal density
- high rate of transpiration
- low specific leaf area
leaves of shade plants
- large and thin
- low stomatal density
- low rate of transpiration
- high specific leaf area
sun plants
- vertical leaf orientation
- leaf area index higher
- more canopy layers
- short leaf lifespan and high turnover
- high photosynthetic capacity
shade plants
- horizontal leaf orientation
- leaf area index lower
- fewer canopy layers
- long leaf lifespan and low turnover
- low photosynthetic capacity
