Transcript Notes- Temperature

Animal, Plant & Soil Science
E4-6
The Influence of Temperature on Plants
Terms
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cardinal temperature range
cool season crops
hardiness
growing degree day (GDD)
metabolism
optimum temperature
plant heat-zone map
plant hardiness zone map
stratification
thermoperiod
thermoperiodic
vernalization
warm season crops
Objectives
 1 Discuss the effect of temperature on plant growth
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and describe plant responses to temperature
extremes.
2 Explain cardinal temperature range for growth and
survival of common plants.
3 Describe plant responses to temperature.
4 Explain plant hardiness and heat tolerance.
5 Explain growing degree days and demonstrate the
ability to calculate growing degree days.
Interest Approach
 Bring a bunch of bananas to class and display them in
view of the students. Some students might ask about the
bananas. Tell them you would like to grow bananas so
you can have fresh bananas throughout the year. This
might be received with skepticism, at which time the
students could be asked what is wrong with that idea. A
series of questions could be asked in response. Is the
local soil not the right type? Is the air not appropriate? Is
there not enough rain? The students will soon identify
temperature as the problem. Continue the discussion by
talking about how plants have adapted to different
temperature ranges.
How does temperature affect plant growth?
 I. Temperature is an important factor
governing plant growth.
 A. Metabolism is the term used to describe all
the chemical reactions in a plant, including
photosynthesis and respiration. 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, whereas warmer temperatures speed
the processes.
How does temperature affect plant growth?
 B. 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. 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 86°F. So, during hot
summer days, plants draw upon stored energy
reserves.
How does temperature affect plant growth?
 1. Some plants are more tolerant of
extreme hot temperatures than others.
The leaves of plants suffering from heat
damage often have a scorched appearance,
and they may drop from some plants.
 2. Leaves and tender shoots of plants
subjected to freezing temperatures may
appear water-soaked and wilted. The
damaged tissues usually turn black within
a few days. The leaves of some plants may
look burned.
What is the cardinal temperature range for growth
and survival of common plants?
 II. The cardinal temperature range is the
temperature range in which plants grow and survive.
There are three important temperature points—the
minimum cardinal temperature, the optimum
temperature, and the maximum cardinal
temperature.
What is the cardinal temperature range for growth
and survival of common plants?
 A. The minimum cardinal temperature for
the growth of most species is 40° to 50°F (5°
to 6°C). At temperatures of 32° to 45°F (0° to
7°C), the health of tender or sensitive plants
may be in jeopardy. Semi-hardy plants may
die when temperatures drop to 15° to 29°F (–
9° to –2°C). Hardy plants may not be injured
until temperatures reach 0°F (–18°C).
What is the cardinal temperature range for growth
and survival of common plants?
 B. Optimum temperature is the ideal
temperature for plant growth.
 1. Cool-season plants grow best at 65° to 75°F (18°
to 24°C). Cool-season plants are grown as fallwinter crops in the southern United States. In the
northern part of the United States, these plants
are grown in late spring, summer, and early fall.
 2. Warm season plants grow best at 78° to 90°F
(24° to 32°C). Warm-season plants are grown in
late spring and summer, early fall in the southern
United States. In the northern part of the United
States, warm-season plants are grown in summer,
but for some warm season crops, the growing
season may be too short for good yields.
What is the cardinal temperature range for growth
and survival of common plants?
 C. Maximum cardinal temperature for the growth of
most plant species is 90° to 96°F (32° to 36°C).
Death of most species occurs at around 130°F
(54°C).
What are some plant responses to temperature?
 III. Different species of plants respond
differently to temperature. Temperatures also
play a role in different plant functions.
 A. 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.
What are some plant responses to temperature?
 B. 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. Warm season crops require
warmer temperatures for best growth.
Cotton, corn, soybeans, and sorghum are
examples of warm season crops. Another
warm season crop, tomatoes, will not flower
if temperatures are cool.
What are some plant responses to temperature?
 C. Some plants require a cold treatment for
physiological processes to occur, which 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 32° and 45°F to break their rest period.
What are some plant responses to temperature?
 D. 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 to
germinate is known as stratification.
What are plant hardiness and heat tolerance?
 IV. Plants can be classified as hardy or non-hardy,
depending on their ability to withstand cold
temperatures. Hardiness is a plant’s ability to
tolerate cold temperatures.
What are plant hardiness and heat tolerance?
 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.
This map is valuable in selecting plants adapted for
growing in each area.
What are plant hardiness and heat tolerance?
 B. 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 was 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 86°F. The temperature at which plants are
unable to process water fast enough to maintain
normal functions is 86°F. Plants also experience
damage to cellular proteins at this temperature.
What is a growing degree day, and how is a growing
degree day calculated?
 V. Growing degree days (GDD) is a measure of
temperature requirements for plants and can be used
to estimate growth and development.
What is a growing degree day, and how is a growing
degree day calculated?
 A. The basic concept of growing degree days is that plant
development will occur when temperatures exceed a base
temperature. For corn, this is the maximum temperature plus
the minimum temperature in a day divided by 2 minus 50.
Fifty is selected as the constant because corn grows very little
at temperatures of 50°F or below. Growth is also checked
when temperatures rise above 86°F, so all temperatures
recorded above 86°F are counted as 86 in the formula. Most
corn hybrids have fairly specific GDD specifications. Example:
If a low temperature was 60°F and the high was 90°F, the
GDD would be 60 + 86 = 146 ÷ 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.
REVIEW
 1. How does temperature affect plant growth?
 2. What is the cardinal
temperature range for
growth and survival of common plants?
 3. What are some plant responses to temperature?
 4. What are plant hardiness and heat tolerance?
 5. What is a growing degree day, and how is a
growing degree day calculated?