C4_2 Plants, Temperature,

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C4_2 Plants, Temperature, Climate
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Terms. The following terms are presented in this
lesson (shown in bold italics)

• Cool season crops
• Hardiness
• Growing degree day (GDD)
• Metabolism
• Plant heat-zone map
• Plant hardiness zone map
• Stratification
• Thermoperiod
• Thermoperiodic
• Vernalization
• Warm season crops

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Objective 1 Discuss the effect of temperature on
plant growth.

• All of the chemical reactions in a plant,
  including photosynthesis and respiration, fall
  under a term, metabolism. The speed at which
  metabolism occurs is affected by temperature.
• This is because the enzymes that drive the
  reactions are sensitive to temperature.
• Cool or cold temperatures slow metabolic
  processes, while warmer temperatures speed
• the processes.

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Objective 1 Discuss the effect of temperature on
plant growth.

• Most plants show optimum growth when night
  temperatures are 10 to 15 degrees cooler
• than day temperatures. Under ideal conditions
  photosynthesis occurs at a high rate during
• the day. The cooler temperatures at night slow
  respiration. For growth to occur, the
• rate of photosynthesis must exceed that of
  respiration.

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Objective 1 Discuss the effect of temperature on
plant growth.

• High temperatures can speed the rate of
  respiration beyond that of photosynthesis.
• As a result, the products of photosynthesis are
  used more rapidly than they are produced.
• In many plants, photosynthesis shuts down at
  temperatures above 86F.
• So, during hot summer days plants draw upon
• stored energy reserves.

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Objective 2 Describe plant responses to
temperature.

• Different species of plants respond differently
  to temperature. Temperatures also play a role
• in different plants functions.
• The change of daily temperatures is called
  thermoperiod. When changes in daily temperatures
  influence plant responses, such as flowering, the
  plants are said to be
• thermoperiodic. Poinsettias and chrysanthemums
  are thermoperiodic plants. They initiate flowers
  when temperatures become cooler and days grow
  shorter.

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Objective 2 Describe plant responses to
temperature.

• Wheat, oats, barley, rye, spinach, and lettuce
  are cool season crops meaning they prefer
• cooler growing temperatures and are tolerant of
  frost. When temperatures rise in combination
• with longer days, spinach and lettuce initiate
  flower production

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Objective 2 Describe plant responses to
temperature.

• Warm season crops require warmer temperatures for
  best growth. Cotton, corn, soybeans, and sorghum
  are an example of a warm season crop. Another
  warm season crop, tomatoes, will not flower if
  temperatures are cool.

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Objective 2 Describe plant responses to
temperature.

• Some plants require a cold treatment for
  physiological processes to occur. This is known
• as vernalization. Tulips and narcissus require
  vernalization to flower.
• Some cereal grains, including winter wheat, also
  require vernalization. Apples require 1,000 to
  1,200 hours of temperatures between 32F and 45F
  to break their rest period.

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Objective 2 Describe plant responses to
temperature.

• Seeds of some plants have a dormancy mechanism
  that is broken by a cold period. The
• seeds do not germinate until the seed has
  undergone a cold period.
• This cold requirement for seeds is known as
  stratification.

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Objective 3 Explain hardiness.

• Plants can be classified as hardy or non-hardy
  depending on their ability to withstand cold
• temperatures. Hardiness is a plants ability to
  tolerate cold temperatures.
• A. The USDA has established a plant hardiness
  zone map for the United States, that reflects
• the average minimum winter temperatures for given
  areas. The map shows eleven
• zones of temperatures. It is valuable in
  selecting plants adapted for growing in those
  areas.

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Objective 3 Explain hardiness.

• Heat also plays a role in the performance of
  plant species. Some plants are more sensitive
• to heat than others. The plant heat-zone map has
  been developed by the American
• Horticultural Society to help identify areas in
  which landscape plants can flourish. The
• map shows 12 zones. Each zone reflects a rating
  of summer heat based on the average
• number of days above 86F.

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Objective 3 Explain hardiness.

• Eighty-six degrees is a temperature at which
  plants are unable to process water fast enough to
  maintain normal functions. Plants also experience
  damage to cellular proteins.

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Objective 4 Explain growing degree days.

• Growing degree days (GDD) is a measure of
  temperature requirements for plants and can
• be used to estimate growth and development.
• A. The basic concept of growing degree days is
  that plant development will occur when
• temperatures exceed a base temperature. For corn,
  the maximum temperature plus the
• minimum temperature in a day divided by 2 minus
  50.

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Objective 4 Explain growing degree days.

• Fifty is selected as the constant because corn
  grows very little at temperatures of 50F or
  below.
• Growth is also checked when temperatures rise
  above 86F, so all temperatures recorded above
  86F are counted as 86 in the formula.
• Most corn hybrids have fairly specific GDD
  specifications.

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Objective 4 Explain growing degree days.

• Example If a low temperature was 60F and the
  high was 90F, the GDD would be 60
• 86 146 divided by 2 73 50 23 GDD. The GDD
  are added during the growing
• season. If a variety of corn required 2,450 GDD,
  it would require 107 days to maturity
• using the figure calculated in the example.