Chapter 9 Photosynthesis:Physiological and ecological considerations

Address the intact leaf under natural conditions

The major environmental factors:

directly: light, temperature, and ambient [CO2],

indirectly: humidity, soil moisture

Physiologists, agronomists, and ecologists

Limiting factors for photosynthesis :

the slowest step determine the rate of photosynthesis

Rubisco activity, ribulose bisphosphate regeneration, triose phosphate metabolism for C3 plants

A “supply” and “demand” function

Three light parameters: spectral quality, amount, and direction

Full sunlight, incandescent light, fluorescent light

watt (W)= J/s

quanta

Systeme International unit, p.200Under direct sunlight 2000 mole m-2s-1

900 Wm-2

Lux or foot-candles: lumen (lm): the luminous flux on a unit surface, all points of which are at unit distance from a uniform point source of one candle. Intensity was expressed either as foot candles (lm ft-2) or lux (lm m-2) based on the perception of light by the human eye, which is maximally sensitive to light within the green region of the spectrum, at 555 nm.

Instruments

calibration

Leaf anatomy maximizes light absorption

fluorescence

About 85 to 90% of PAR is

absorbed by leaf

Transparent to visible light and

convex (focus light) at epidermal

cells

Palisade cells: light to pass through

sieve effect: chlorophyll is confined to the chloroplasts

light channeling: through the central of vacuole and air space between the cells

Spongy cells: light absorption

light scattering: increase the travel length

Hairs, salt glands, and

epicuticular wax (reflect light)

C3

Plant compete for sunlight A canopy configuration

A rosette growth: leaves grow radially A branching structure: increase interception

Sunflceks: one of the characteristics of shade plants capture a short burst of sunlight

dandelion

Solar tracking:

The leaf blade is perpendicular to the incident light

alfalfa, cotton, soybean, bean, lupine, and mallow family

Circadian rhythms: sun rise, sun set; intermittent cloud, night/dawn

a blue-light response of leaf movement

Photosensitive region: major leaf veins

Pulvinus: is the organ to control the leaf orientation, at the junction between the blade and petiole

Heliotropism: paraheliotropic vs. diaheliotropic (short-lived plants)

Lupinus succulentus

向日葵 ?

Pulvinus: at the junction between the blade and petiole

The mechanism of leaf movement – a rapid response to phytochrome involving ion fluxes across membranes causes

turgor changes

pH change also involve

Plant acclimate and adapt to sun and shade

p. 672

If tolerance increases as a result of exposure to prior stress,

the plant is said to be acclimated (or hardened)

environmental

A genetically determined level of resistance acquired by a

process of selection over many generations is adaptation

genetic

p. 203

Glossary

Photosynthetic responses to light by the intact leaf

Light compensation point (LCP): the photon flux when photosynthetic CO2 assimilation equal to CO2 release by mitochondria respiration

LCP varied with species and developmental conditions

A C3 plant The carboxylation capacity of rubisco or the metabolism of triose phosphates

Light compensation pointSun plants:

10~20 μmole m-2 s-1

Shade plants: 1~5 μmole m-2 s-1

Maximal photosynthetic rate

sun shade plants

Maximum quantum yield

the slope (p. 131)

saturation

Quantum yield: No. of photochemical products / Total No. of quanta absorbed

Gas solubility/ temp

C4 plants: CO2 concentration

C3 plants: photorespiration

lower temp, higher

quantum yield

Growth conditions affect the photosynthetic properties of a leaf