Ch. 2 Photosynthesis (Ps) and Light. CAM and Epiphytes Epiphytes: –Abundant tropical rain forests

Ch. 2 Photosynthesis (Ps) and Light

CAM and Epiphytes• Epiphytes:

– Abundant tropical rain forests

CAM and Epiphytes• Spanish moss (Tillandsia

usneoides)• CAM plant:

Comparing C3, C4, CAM plants• Exs: many Orchidaceae

(esp. epiphytes)

Comparing C3, C4, CAM plants• CAM:

– Succulents (deserts)– Epiphytes (tropical/subtropical areas)

Comparing C3, C4, CAM plants• Trait C3 C4 CAM

• Max. Ps rate

Fig. 2.12

Comparing C3, C4, CAM plants• Trait C3 C4 CAM

• Max. growth rate• (optimal conditions)

Comparing C3, C4, CAM plants• Trait C3 C4 CAM

• Optimum Ps temp.• .

Fig. 2.11

Comparing C3, C4, CAM plants• Trait C3 C4 CAM

• Water use efficiency

(g CO2 gain per

Kg H2O lost)

Applied Aspects• What crops best hot areas?

sorghum

millet

Applied Aspect• Genetic engineering:

Applied Aspect• Ex: rice (C3 grass)

• Asia: 70% calories rice– 70% world’s poor Asian

• Put in– Yields up 10-30%

C3 variation (between species)• C3 plants

• Heliophytes:• Sciophytes:

Sciophyte: Who am I?Variation among C3 plants

C3 variation (within individual)• Sun vs. shade leaves• Sun leaves:

Quercus pagoda (cherrybark oak)

European beech

Sun Shade

Carbon isotope ratios• Isotope:• Ex: Carbon-12 (98.9% C)• Carbon-13• Carbon-14

Light vs. heavyCarbon dioxide

Enzyme affinity?

Carbon isotope ratios• Enzyme affinity

– If low, light CO2 used more (more discrimination)– If high, less discrimination

Carbon isotope ratios• Enzyme affinity

– If low, light CO2 used more (more discrimination)– If high, less discrimination

• Measure ratio? Delta C-13– Units:– More negative delta C-13 =

Carbon isotope ratios• Enzyme affinity CO2

– Rubisco: less– PEP carboxylase: more

• C3 delta C-13; -24 to -34 ppt• C4 delta C-13; -10 to -20 ppt

More negative = more discrimination

C4

SO WHAT??Commercial sugar (sucrose):• Sugar cane• Sugar beet

AHAH!ID sugar source delta C-13 ratio!

• C3: -24 to -34 ppt• C4: -10 to -20 ppt

Bernie Beet hands out sacksof white powder to kids.....

Bernie BeetFood webs….

Herbivore Feeding PreferencesEx., rhinos AfricaBlack rhino: more rare (3,600). Browses

Herbivore Feeding PreferencesWhite rhino: less rare (11,700). Grazes

Herbivore Feeding PreferencesRhino poaching: ID horn using delta C-13 ratio

Ch. 3 Water Relations & Energy Dynamics

Water relations• Plants need light (energy: Ch. 2)

• Plants need CO2 (carbon: Ch. 2)

• Plants need water (Ch. 3)

Water potential

Water potential• Water potential:

• “Tendency water to move”– Moves

• Symbol--Greek letter: psi

4 factors that influence water potential

Water Potential• Affected by:

– solutes: solute potential– symbolized– high solutes =

s

Water Potential• Affected by:

– pressure: pressure potential – symbolized – high pressure =

p

Water Potential• Affected by:

– charged surfaces (cell walls, clay particles): matric potential

– symbolized – More surfaces =

m

The Matrix potential

Water Potential• Affected by:

– gravity: gravitational potential– symbolized – Height increases, tendency move

g

Water Potential• Total water potential = sum all factors:

g= + + +total mps

Units?

Water Potential• Measurement relative: compared to

• = 0 megaPascals (MPa)

• megaPascal:

– 1 MPa = about 10 bars or 10 atmospheres

total

Water Potential• Water in plants/soil has solutes: so

What tissue in plant carries water?

Water transport• Xylem:

• What % water from soil remains in plant?

Water transport• Xylem: water

conducting tissue• How much water in

plant? <5%!

How water move?

?

Water transport• Transpiration:

• Moves by pull (under tension)

• Psi high soil & low air.

Water transport• Ex: • Soil:• Root xylem: • Stem xylem:

• Leaf xylem: • Air: -10 to -100 MPa

Water potential tour.....• Soil to air pathway

Fig. 3.2a

Soil water

• What determines psi soil?

g= + + +total mps

Soil water

• What determines psi soil?• gravitational potential:

• pressure potential:

g= + + +total mps

Soil water

• solute potential:

g= + + +total mps

Dauphin Island: salt marsh

Soil water

• matric potential:

g= + + +total mps