lec #4 what is the minimum amount light a plant

7/30/2019 Lec #4 What is the Minimum Amount Light a Plant

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What is the minimum amount

light a plant will need?

Plant Physiology

Lecture #31-26-09

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8- to 120mmol m-2S-1

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What is meant by photoperiod?

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It refers to the duration interms of day length

classification (short day, long day, day neutral

plants)

A response of flowering

The amount of daylight (length) duration

needed for a plant to flower.

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Why do plant flower in response

to light?

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Because of phytochrome

Plant color

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Distinguish between the two

main phytochromes.

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Pr = absorbs red light at 680 nm

Pfr = absorbs far red light at 730 nm

These are photo reversible

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Discuss the 3 developmental

response of plants to light

(red: far red)

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Seed germination Related to seed in forest

Seeds that response to light to germinate Which do not get much light = low light

Germinates when there is a gap in forest cannopy Evasion (most leaves absorb blue/red light)

Purslane evades far red light

Morphology Plants grow in narrow spacing and high density

Longer internodes Few branches

Related to low R:Fr ratio

More biomass

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What is negative phototropism?

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Plant growing away from light (because of the

quality of the light as appose to the intensity)

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Discuss the plant nutrient needs.

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Plants absorbs more than 90 nutrients

About 17 are essential

13 used in large amounts

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Show in order of abundance the 6

important minerals needed for plant

growth

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N> K> Ca> Mg> P> S

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What 3 elements makes up 95%

of plant needs?

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C , H, O

They produce carbohydrates in plants

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Give an example of a mineral

that is toxic to plants.

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Pb

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List three essential criteria for

plant nutrients

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1. A lack will stop plant growth

2. Elements is directly involved in nutrition of

plants and not merely taking up space.

3. A shortage can be corrected only by

supplying that element.

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Discuss a plants response to N.

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N speeds up growth

Produce dark green leaves

High protein content Improves water use when

there is an ample supply

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Lists ion picked up by plants in

abundance.

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NO3-

NH4+

HPO4-2

H2PO4-

K

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What happens with too much N?

list six adverse effects ?

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Soft weak and easily injured

More prone to disease

Overly rapid growth and slows maturity Delays hardening off (reducing water

application )

Impairs flowering in vegetable crops Increases risks to humans

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How does too much nitrogen in

plants increase risks to human?

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Oxalic acid

Interferes with Ca++ absorption

Methemoglobinia

Blue-baby syndrome

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lec #4 what is the minimum amount light a plant

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