Download Horticulture Science

Understanding Light,
Temperature, Air, and Water
Effects on Plant
Growth
•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 heatzone 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