Leaf Reflectance & Absorption

Leaf Reflectance & Absorption “Pimple” Savanna forms from termite mounds in innundated tropical grasslands

Beltsville winter wheat

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

Plant Pigments 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 Absorption Liquid water in plant leaves completes the absorption picture: leaves must be hydrated for photosynthesis

Green Leaf Structure

Dicot and Conifer Leaves Bean leaf x420 Pine needle x370

Maple & Pine reflectancel Similar in visible light, different in the near-IR maple pine

Leaf Reflectance & Absorption Banana x1400 Cucumber x490

Leaf Photosynthesis Photosynthesis Determines Optical Properties Bean leaf x4200

Leaf Photosynthesis Photosynthesis Determines Optical Properties Must capture photons to drive chemical reactions (energy input) Must be in presence of H2O Must be in presence of CO2 Must get rid of O2 (poisonous) Must live in hostile setting…

Internal Leaf Structure Intercellular air labyrinth CO2 in & O2 out Chloroplasts

Leaf Reflectance & Absorption Photosynthesis 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

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

Leaf Photosynthesis Piers Seller’s PAR Diagram

Photosynthesis Action Spectrum