Ch 2 Light and Photosynthesis Ps Light Radiant

Ch. 2 Light and Photosynthesis (Ps)

Light • Radiant energy (electromagnetic radiation) – Particle + wave • Particle: torp

Light • Wave: has • Wavelength inversely

Light • Visible light: 380 -750 nanometers (nm) (nano=10 -9)

Electromagnetic spectrum • T/F: Plants green because chlorophyll absorbs green light

Electromagnetic spectrum • 400 -700 nm: Photosynthetically Active Radiation (PAR) – Drives Ps – Green least (why leaves green) Action spectrum for photosynthesis (Ps)

Radiation • • Helps determine IR: 750 -106 nm. Objects > absolute 0 emit Gain energy from IR too Pred

IR • “Infrared (IR) window” of leaves • Transmit near IR (beyond visible): little • Most visible IR window

IR • Near IR transmitted through leaves (dashed line)

IR • Use IR window (sense overstory)? ? • First: phytochrome

Phytochrome • 2 forms (interconvertible) • Pr absorbs R: converted to Pfr • Pfr absorbs FR (near IR): converted to Pr • Pfr active

IR • 1) Ratio Pr: Pfr depends on ratio R: FR light • 2) R: FR influenced by leaves – Leaves remove R, let FR through “IR window”

IR • Ex, red alder (Alnus rubra) • Germination sensitive to Pfr – Pfr high: – Pfr low:

IR • Ex, red alder (Alnus rubra) • In open: lots R light, lots Pfr

IR • Ex, red alder (Alnus rubra) • Under canopy: lots FR light, less Pfr

IR • Plants may use phytochrome – 1) shaded: stimulate etiolation (spindly, less chlorophyll) – 2) info on canopy (deciduous forest) Trillium

Electromagnetic spectrum • UV radiation: < 350 nm (to 1 nm)

UV • Danger: Damage DNA (skin cancer!) • Pigments (ex, flavonoids) absorb • +DNA repair mechanisms Diamorpha smallii

Units (Intensity) • ?

Units

Units • PAR: Photosynthetic Photon Flux Density (PPFD) • moles photons/sq. m/sec National Mole Day? ?

Units PPFD • 1 mole photons = 1 Einstein • So, Einsteins/sq. m/sec National Mole Day? ?

Light intensity variation • Canopies patchy in

Light intensity variation • Phenoseason: seasonal light change + canopy change Max. lite canopy top Max. lite ground level

Phenoseasons • Ex, Eastern Deciduous Forest understory plants • 4 strategies: • 1) Spring herbs (“Ea”): emerge early Canopy leaf expansion Canopy leaf drop

Spring herbs Ex, Trillium

Spring herbs Ex, Erythronium (trout lily)

2. Summer green herbs • Emerge late spring, green summer, dormant fall • “Us” Canopy leaf drop Canopy leaf expansion

Summer green herbs • Ex, Uvularia sessilifolia (bellwort) Uvula? ?

Summer green herbs • Ex, Uvularia sessilifolia (bellwort)

3. Late-summer herbs • Emerge summer, get early fall sun (Aa) • Ex, Aster acuminatus (sharp-leaved aster) Canopy leaf drop Canopy leaf expansion

4. Semievergreens • Emerge late spring, green late: “Om” • Ex, Oxalis montana (wood sorrel) Canopy leaf drop Canopy leaf expansion

Light variation • Canopies patchy • Question: Technical name for beam sunlight on forest floor?

Light variation • Canopies patchy in space • ______: beam sunlight on forest floor

Sunflecks: Good • Useful (forest floor plants) – Some: 70% energy sunflecks

Sunflecks: Good • Useful (forest floor plants) – Some: 70% energy sunflecks • Ability to use: – Spring herbs (Trillium) respond – Summer green herbs (Uvularia) exploit

Sunflecks: Bad – Ex: shade-adapted Oxalis. Redwood forest (Oxalis oregana-redwood sorrel) – Coast redwood (Sequoia sempervirens) • Tallest tree: 368 ft. DBH 23 ft. !

Sunflecks: Bad • O. oregana: Sunflecks damage Ps machinery

Sunflecks: Bad • Sunflecks & drought stress • Ex, regeneration Abies magnifica (CA red fir)

Sunflecks • Ex, regeneration Abies magnifica (CA red fir) • Seedling pattern from sunfleck pattern