animal, plant & soil scienceanimal, plant & soil science e4-6 the influence of temperature...

Animal, Plant & Soil ScienceAnimal, Plant & Soil Science

E4-6The Influence of Temperature on

Plants

Terms

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 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.


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.


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.


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).


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 fall-winter 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.


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.


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.


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.


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.


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.


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?