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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
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