LeafLeaf Reflectance & Absorption Reflectance & Absorption

““Pimple” SavannaPimple” Savannaforms from termite mounds in forms from termite mounds in innundated tropical grasslandsinnundated tropical grasslands

LeafLeaf Reflectance & Absorption Reflectance & Absorption

Beltsville winter wheatBeltsville winter wheat

True & False Color PhotosTrue & False Color PhotosIn true-color, grass and astroturf look similar; in the near-infrared, grass is more reflective

grass

astroturf

astroturfastroturf

grass

TrueTrue colorcolor filmfilm

ColorColor infraredinfrared filmfilm

Plant PigmentsPlant PigmentsSo, what absorbs in functioning leaves?So, what absorbs in functioning leaves?

None of the key pigments absorbs green light; instead it is reflected to our eyes, which makes plants look green to us.

Liquid Water AbsorptionLiquid Water Absorption

Liquid water in Liquid water in plant leaves plant leaves completes the completes the absorption absorption picture: leaves picture: leaves must be must be hydrated for hydrated for photosynthesisphotosynthesis

Green LeafGreen Leaf StructureStructure

Dicot and Conifer LeavesDicot and Conifer Leaves

Bean leaf x420Bean leaf x420 Pine needle x370

Maple & Pine reflectanceMaple & Pine reflectance

maple

pine

Similar in visible light, different in the near-IR

LeafLeaf Reflectance & Absorption Reflectance & AbsorptionReflectance = 1.0 - Absorption

Banana x1400 Cucumber x490

Leaf PhotosynthesisLeaf PhotosynthesisPhotosynthesis Determines Optical Properties

Bean leaf x4200

Leaf PhotosynthesisLeaf PhotosynthesisPhotosynthesis Determines Optical Properties

Must capture photons to drive Must capture photons to drive chemical reactions (energy input)chemical reactions (energy input)

Must be in presence of H2OMust be in presence of H2O

Must be in presence of CO2Must be in presence of CO2

Must get rid of O2 (poisonous)Must get rid of O2 (poisonous)

Must live in hostile setting…Must live in hostile setting…

Internal Leaf StructureInternal Leaf Structure

ChloroplastsIntercellular air labyrinth CO2 in & O2 out

LeafLeaf Reflectance & Absorption Reflectance & AbsorptionPhotosynthesis requires CO2 from atmosphere to be in contact with the plant cell surfaces. The intercellular labyrinth allows movement of CO2 into leaves and O2 out. Part of the “deal” is H2O is lost

LeafLeaf Photosynthesis Photosynthesis

Stomata regulate gas exchange and water loss CO2 in/O2 out

LeafLeaf Photosynthesis Photosynthesis Piers Seller’s PAR DiagramPiers Seller’s PAR Diagram

Photosynthesis Action SpectrumPhotosynthesis Action Spectrum