L8 - Leaf Angles and Canopy Light Distribution Flashcards
Give two ways in which plants can avoid excess light in the short term (minutes to days). Provide examples for each.
1) Shade species show rapid leaf movements e.g. temporary changes in leaf angle.
- Oxalis oregana showed rapid changes in leaf angle upon high light exposure.
2) Some plants alter reflectance of light e.g through trichomes.
- Atriplex hymenelytra reflectance decreases as it’s rehydrated over 3 days.
Give two ways in which plants can avoid excess light in the long term. Provide examples for each.
1) Species can develop with leaf angles that minimise light absorption.
- Shrubs and herbs: leaf angle increased when there was a decrease in water.
- Shown through 159 species on precipitation and elevation transect in Utah.
- Draw sketches seen on pg 10 of angle vs precipitation.
2) Leaf surface reflectance can increase due to pubescence growth.
- Encelia californica, found in moist climate (Cali coast), has normal absorption profile.
- Encelia farinosa, found in desert, has lots of leaf hairs, decreasing absorption by 50% compared to E. californica.
- Additionally, hairiness in E. farinosa increased as season got progressively drier.
Give four ways in which species make sure enough light is being absorbed, especially for understory species.
1) Capitalise on sunflecks - can account for a large amount of photosynthesis.
2) Diaheliotropism, where leaves remain perpendicular to sun’s rays, max. light capture.
- Solar tracking by species increases with shorter growing season.
- E.g Desert winter annuals: rain 15-20 weeks, 28% track
- Desert summer annuals: rain 5-15 weeks, 75% track.
3) Reacting to formation of gaps from e.g wind damage, tree death etc… two strategies:
- Germinators: germinate when gap forms, typically shade intolerant pioneer species.
- Persistors: germinate and wait as seedlings for gap, typically shade tolerant species.
4) Altering growing season to match light availability.
- E.g spring flowers in temperate woodland develop before canopy closes.
- Winter green species develop after canopy has gone.
Give two factors that can impact canopy density and why this factor is important.
- Leaf arrangement (clumped or regular separation)
- Angle of the leaves (erectophilous or planophilous), more detail later.
Important as for most canopy plants there is more light at canopy top than is usable. So light distribution down canopy is important, influenced by canopy density.
How is canopy density/leafiness measured?
How does this influence productivity?
How do erectophilous and planophilous plants compare on this scale?
- Leaf Area Index (m2 leaf per m2 ground) used.
- Higher LAI communities typically more productive.
- Erectophilous = high LAI generally.
- Planophilous = low LAI generally.
What factors does attenuation depend on?
Give some comparisons between plant groups.
Sketch the relevant diagram
- Depends on canopy structure, not just LAI.
- Grasses attenuate more gradually with increasing LAI than broadleaved dicots (very planophilous)
- Diagram on pg 13. Note log scale.
What technologies can be used to asses forest canopy structure?
- LIDAR technology, where light is reflected off canopies from a plane.
How do canopy structures develop over time?
- Leaves packed in narrow height band in young stands.
- As they mature, leaves spread out over wider range.
How does leaf angle typically vary throughout the canopy?
How does leaf N content typically vary throughout the canopy?
Leaf angle increases with canopy height.
-Top leaves likely don’t need to optimise for light capture.
- Maximises absorption throughout canopy (by not shading out lower leaves).
Leaf N content increases with canopy height.
- Carbon assimilation in lower leaves limited by light, not N.
- Better to invest N into higher leaves that receive more light where increased N will cause increased carbon assimilation.
