Photosynthetically Active Radiation

MJm2d-1

Only accounts for visible radiation

Can change PAR by changing location and planting date

Caopy absorption of radiation

Fraction of light that is actually absorbed by the plant

Shows the relationship between leaf position and radiation

Radiation Use Efficiency 

g per MJ1

How efficiently solar radiation is converted into biomass

Impacted by temperature (how much biomass is made per unit of radiation absorbed)

Leaf Area Index

This is the single sided leaf area per unit ground area

As more leaf area is accumulated, each leaf intercepts less

The yield equation

Harvest Index

proportion of total crop dry matter that is allocated to the harvested portion of the crop 

Short Season Variety

- if you choose a short variety in a long season, there will be early maturity

- Thus, total time for dry matter accumulation (PAR, ac and RUE) is less

Long Variety in Early Frost

- If frost occurs before the grain filling stage, HI will be lower than normal

Low Planting Density

- reduces plant stand, hence PAR is limited

- Not a lot of leaf area will develop, so alpha c is limited too

High Planting Density

- HI will be low

- Too much vegetative growth and not enough resources used to establish seed and grain filling

Reduces rate of leaf area expansion (alpha c decreaed)

Stomatal closure, so CO2 availability is limited (photosynthetic rate is dropped, so RUE is impacted)

 1. Rapid water uptake

- Most physiological transitions occur

- See cell electrolyte loss because membrane is "leaky"

2. Lag Phase

- Rate of water uptake has slowed down

3. Final phase

- Seed axis becomes hydrated again to lead to germination 

Hypogeal

- cotyledons are below ground

- All monocots

Epigeal

- cotyledons are above ground

- too much mechanical impedence can be bad (hypocotyl hook has to pull)

- Not all dicots 

Yes

rate of respiration increases dramatically. It is needed to mobilize energy reserves from the seed

High CO2 levels inhibit seed germination

Some yes.

Seeds that are POSITIVELY PHOTOBLASTIC need light expsure or else they will not germinate

It is a pigment that changes red light to far-red

far red to red over night, but can be changed back to red quickly if a flash of far red goes off

far red promotes germination

Heterotrophic growth (energy is suppled by seed storage reserves) to autotrophic growth (energy provided by photosynthesis)

During grain filling, energy reserves are stored in endosperm. As the seed dries, these reserves run out

Critical period because once seed reserves are depleted, total seedling energy reserves can get very low if leaves cannot develop for photosynthesis 

1. Exponential Growth

- Accelerated Vegetative growth

- Photosynthetic machinery developed here

- Leaf area is expanding (but law of diminishing returns)

- Slow initially because no leaf growth

2. Linear Growth

- Rate of dry matter accumulation is constant 

3. Senescence

- Photosyntheic capacity of leaves declines (RUE decreasing) because no new leaves are made

- 

Finger-like leaves

Makes light more diffused (evenly spread throughout the canopy)

Photosynthesis is higher

RUE is decreasing

Canopy uses the intercepted light less efficiently because upper leaves are losing photosynthetic capacity