Understanding Light, Temperature, Air, and Water

Effects on PlantGrowth

Understanding Light, Temperature, Air, and Water

Effects on PlantGrowth

•Examine the effect of light on plants.•Describe a plant’s temperature needs.•Explain how the quality of air affects plants.•Determine a plant’s water needs.

How does light affect plants?

• The sun emits a wide range of radiation – light we see = visible light

• Visible light drives photosynthesis• Sunlight contains a complete blend of all

visible colors– Plants need mostly the colors blue and red to

activate the chlorophyll

How does light affect plants?

• Different colors of light solicit different plant responses– Red light promotes seed germination, seedling

growth, stem elongation, and influence flowering

– Blue light reduces stem length, increases branching, promotes stem strength, can improve leaf and flower color

How does light affect plants?

– Far-red light triggers a shade avoidance response in plants when levels of blue or red light are low. • Stems stretch and become weak • Leaves become thinner and wider • Can break seed dormancy

How does light affect plants?• Light intensity impacts plant growth

– High light intensity elevates the rate of photosynthesis

• the plant is able to produce more food

• Intensity of light depends on – Angle of the sun– Clouds – Dust

• Light intensity is greater in the summer

How does light affect plants?

– Plants receiving the optimum level of light will be compact and have good leaf color. • Symptoms of lower than optimum light

levels include a slower growth rate, thin leaves, small flowers, dull leaf and flower color, and etiolation or stretching.

• Extended periods of cloud cover can slow crop growth and ultimately reduce yields.

How does light affect plants?

• Some plants have a photoreceptor or light-sensitive pigment that absorbs light– Allows plant to respond to amount of light– Length of the day (amount of light) can

influence • different phases of plant growth• flowering• seed germination • enlargement of leaves• development of buds

What temperatures are best for plants?

• Plants change depending on the temperature– Higher temps = smaller leaves in lighter colors

with thicker cuticles– Low temps = growing lower to the ground with

short life cycles and parabolic dish-shaped flowers to collect light and heat.

• Plants prefer temperatures between 32°F to 100°F

What temperatures are best for plants?

• A plant’s ability to withstand low temperatures is called its hardiness. – A very hardy plant can survive in a cold

climate.

• Each area of the country is assigned a zone number (1 to 10).

• Hardiness zones are derived from the average coldest temperatures for the year.

What temperatures are best for plants?

• Heat affects on plants– At 86°F plants are unable to process water fast

enough to maintain normal functions

• Information used to create plant heat-zone map– The map shows 12 zones

• Wilting– lose water faster than it can be replaced

• Without an exchange of gases, photosynthesis shuts down

What temperatures are best

for plants?

How does the quality of air affect plants?

• Air contains carbon dioxide and oxygen, both of which are necessary for plant growth.– Oxygen necessary for cellular respiration

• picked up mainly by the roots

– Carbon dioxide is used for photosynthesis• Picked up mainly by the leaves

How does the quality of air affect plants?

• Humidity, which is water vapor in the air, affects plant growth. – High humidity = increased growth rate

• Helps photosynthesis function smoothly

– Low humidity = stress on the plant

• One drawback of excessive humidity is the increase of leaf and flower diseases

How does the quality of air affect plants?

• Dust in the air can reduce light intensity slowing photosynthesis.

• Chemical pollutants, such as sulfur dioxide and ozone, can actually kill plant cells or the entire plant.

How do plants get water?

• Plants receive most water through the root system– Life processes (photosynthesis and

respiration) of plants depend on water– Minerals are only absorbed if they are

dissolved in water – Water also comprises a large percentage

of the plant cells, tissues, and organs.

How do plants get water?

• Timing of watering is critical. – Too frequent = soil too

wet • Damaged plant roots

caused by the lack of good air exchange

– Not enough = root death • Lower the quality of the

crop

How do plants get water?

• Plants in containers – Pots should have drainage holes

• Allow water to drain • Allow oxygen into the root zone

• Good rule of thumb– Water plants thoroughly only when soil is dry

How do plants get water?

• Water should have a favorable pH range – 5.8 to 6.2 is best for most plant growth

• Water should have a desirable range of soluble salts – Soluble salts are dissolved minerals – High levels of soluble salts damages roots