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 ground level

Max. litecanopytop

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

Canopy leaf dropCanopy leaf expansion

Spring herbsEx, Trillium

Spring herbsEx, Erythronium (trout lily)

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

Canopy leaf expansionCanopy leaf drop

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 expansion

Canopy leaf drop

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

Canopy leaf expansionCanopy leaf drop

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