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 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