- - AGRICULTURE CORE CURRICULUM - - (CLF6000) Advanced Core Cluster: ORNAMENTAL HORTICULTURE (CLF6200) Unit Title: PLANT PHYSIOLOGY AND GROWTH ____________________________________________________________________________ (CLF6203) Topic: GROWTH Time Taught in Year(s) REQUIREMENTS 3 hours 3 and 4 ____________________________________________________________________________ Topic Objectives: Upon completion of this lesson the student will be able to: Learning Outcome #: (C-6) - Discuss the environmental factors affecting growth (e.g., light, temperature, soil, humidity, wind, mineral elements, gases, and support). Have students conduct plot tests to determine environmental effects on young plants. ################################################### # The following is provided as supplemental # # material (i.e., review from the Basic Core) # # and should be used as seems appropriate to the # # instructor. # ################################################### Special Materials and Equipment: Flat containers and seeds of various ornamentals. References: Hartmann, H. T., Flocker, W. J., & Kofranek, A. M. (1981). PLANT SCIENCE: GROWTH, DEVELOPMENT, AND UTILIZATION OF CULTIVATED PLANTS. Englewood Cliffs, NJ: Prentice-Hall. Evaluation: Quiz by instructor TOPIC PRESENTATION: GROWTH REQUIREMENTS A. There are six basic growth requirements for plants: heat, minerals nutrients, water, light, gases, and support. B. The distribution of agricultural crop plants in the world is determined by the climate. 1. Temperature, moisture, and light determine where, when, and what plants will grow. 2. Climate is the summation of an area's weather: Weather is short- term, climate is long-term. a. Climate is the fundamental force in the free environment. 1) It shapes the soil. 2) Over a very long period of time, it determine the configuration of the earth's surface. C. Temperature (heat) requirements. 1. Growers depend on climatic records of their area to predict the dates of the last killing frost in the spring and the first killing frost in the fall. a. The time between the last killing frost in the spring and the first killing frost in the fall is the growing period. b. The greater the distance from the equator, the fewer "growing days" are available. c. All plants have optimum temperatures for maximum growth and flowering. 2. Most temperate zone plants grow between temperatures of 39 and 122 degrees Fahrenheit. a. These are generally the limits of plant growth. b. High temperatures alter the structure of active cells, leading to abnormal metabolism and death. c. Strong light raises plant temperatures because the absorbing leaves convert some light to heat. d. Plant parts are injured by high temperatures even when exposed for a short time. e. Low temperatures (above freezing) prevent plants from growing because cells need moderate amounts of heat energy to conduct metabolic processes. f. Freezing kills plant cells. 1) Frost kills because ice crystals disrupt the delicate structure of living cells. 2) Freezing (and thawing) of water within plant cells causes the cell wall to burst and the cell to die. 3) Dormant seeds can survive freezing because they contain much less water than active plants. g. Low temperature injury is evident after the first killing frost in the fall. 1) As the sun shines on the leaves the following day, the damage is observed as blackened leaves. 2) Several frost protection methods can be successfully used. 3) These would include the use of wind machines, orchard heaters, irrigation techniques, and the use of various covers. 3. Plants of different species vary widely in their tolerance of temperature extremes. a. Some algae survive temperatures of 194 degrees Farenheit. b. Some arctic plants survive temperatures of -85 degrees Farenheit. 4. The minimum and maximum temperatures to support plant growth generally are between 40 and 120 degrees Fahrenheit. 5. The temperature at which optimum growth occurs varies with the plant and differs with the stage of development. 6. Most plants require a lower night than day temperature. 7. Some plants require a cold season to complete their annual life cycle. 8. There are various types of injury associated with extremes in temperature. a. Crop losses due to frost can often be avoided by using various frost protection practices. b. The use of hot caps, mulches, wind machines, heaters, and irrigation have all been useful in preventing frost damage. D. Water is one of the most important factors affecting plant growth. 1. Growing plant organs contain about 90 percent water. 2. Water is one of the raw materials for photosynthesis. 3. Over 99 percent of the water entering a plant escapes through transpiration. 4. The presence of large amounts of sodium or chlorine in the water can be toxic to plants. 5. The amount of water necessary depends on the crop as well as the available sunshine during the season. 6. Water is necessary to maintain the functioning of living cells; dehydration kills chiefly because it disupts this functioning. 7. Water also serves as a medium for storing and transporting materials. Most of the materials made by plants dissolve in water. 8. Plant growth is based on water uptake by cells. Most of the volume of young tissue is water. E. Light has many influences on plants. 1. Light provides the energy for photosynthesis. 2. It affects seed germination. 3. It affects flower initiation and flowering. 4. It affects plant movement (phototropism). 5. Light affects differentiation of many tissues and organs. 6. Light control has an important role in agriculture. a. The control of plant density is a method of controlling the amount of light received by plants. b. Some pruning practices are based on controlling competition for light within the plant to affect the crop size and quality. c. The reduction of light by shading is useful in many nursery operations. 2. Plants also use light as a signal to adjust their growth in ways that promote survival. a. Many small wild seeds require light before they will germinate. This delays germination until competing plants are removed. b. Some large seeds will not germinate in the light. This delays germination until the seeds are buried, reducing the chance of becoming dehydrated. c. Shoots orient their growth toward light (phototropism). Some roots grow away from light. d. When kept in darkness, plants adopt a special pattern of growth called the etiolation syndrome. 1) Etiolated shoots grow very fast and are brittle. They do not branch, and the leaves remain small and yellow. 2) These traits improve the plant's chance of reaching light before its food reserves are exhausted. e. If sun-loving plants are grown in the shade of other plants, they adopt a shade-growth syndrome. Growing rapidly on reserve foods, they develop a spindly, unbranched stem and thin leaves. This helps them to escape from the shade. 1) Shade growth results from a pigment called phytochrome that detects the difference in light color between open sunlight and shade by plants. 2) Leaves absorb red light, letting most other colors pass through. 3) Because of shade growth, nursery plants that are grown in dense stands tend to be spindly. 4) Artificial lights often have mixtures of colors that lead to shade-growth. Supplemental lighting may be needed to produce sun-growth. 5) Light quality is not easily altered for outdoor plants, but wider spacing can improve growth by reducing shading. f. Many plants use the seasonal variation in night-lengths to time the formation of storage organs and flowers. 1) This allows plants to prepare for winter before cold sets in, and to time flowering so that related plants flower at the same time, when pollinators are present. 2) The number of hours of light during the 24-hour day is called the photoperiod. In the northern hemisphere, photoperiods lengthen from December 21 to June 21, and they shorten from June 21 to December 21. 3) With respect to flowering, most plants fall into one of three classes: a) Day-neutral plants flower when mature, regardless of photoperiod. b) Long-day plants initiate flowers when the photoperiods become longer than a critical value (the critical daylength). Examples are beets, lettuce, and spinach. In nature, they usually flower between early spring and midsummer. c) Short-day plants initiate flowers when the photoperiods become shorter than a critical value. Examples are chrysanthemum and poinsettia. In nature, they usually flower from late summer through midwinter. d) The critical daylength varies from one species to another, and may be anywhere from 8 hours to 16 hours at temperate latitudes. F. Air movement patterns in the atmosphere are the result of the sun's radiation striking more directly on the tropical regions (near the equator) and less on the polar regions. 1. The direction of the air flow is affected by several factors. a. Warmer air at the equator rises and moves toward the poles. b. The earth spins from west to east. c. There are differences in heating and cooling between land and water masses. d. There are differences in elevation. e. Mountain ranges and valleys give more variation. 2. The final result of these interreactions is the establishment of regions, large and small, with a wide variety of climatic patterns. 3. Winds can be devastating to plants at critical times such as bloom and pollination periods, or during early stages of leaf or fruit growth. G. The two gases most important for the growth of plants are oxygen (02) and carbon dioxide (C02). 1. Oxygen is important in the respiration of all plant parts. 2. Plants use C02 for photosynthesis and they return 02 to the atmosphere. 3. Both plants and animals use 02 and give off C02 during respiration. 4. Pollutant gases in the air can be harmful to plants. a. The burning of fossil fuels adds these polluting gases to the air. b. Some of the harmful pollutants are ozone, nitrogen oxides, sulfur dioxide, fluorides, and ethylene. H. Several vegetables, grapes, fruit trees, and ornamentals require no physical support for best quality and profitable production. 1. Vegetable plants such as wisteria, forsythia, bougainvillea are often staked or trellised for ease of culture and harvest. 2. Most grapevines are trained to trellises to improve berry quality and ease of harvest. 3. Many deciduous fruit trees are wired, roped, or propped to prevent limb breakage. I. Some ornamentals are placed on trellises or arbors to gain maximum advantage of their foliage and flower characteristics. __________________________________________________________ ACTIVITY: 1. Have students do plot tests to observe the environmental effects of temperature, rainfall (irrigation), light, and air movement. __________________________________________________________ 12/14/90 PJK/sg #%&C