- - AGRICULTURE CORE CURRICULUM - - (CLF7000) Advanced Core Cluster: PLANT AND SOIL SCIENCE (CLF7200) Unit Title: PLANT PHYSIOLOGY AND GROWTH ____________________________________________________________________________ (CLF7204) Topic: CLIMATIC FACTORS Time Taught in Year(s) AFFECTING PLANT GROWTH 4 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 plant growth (e.g., temperature, water and humidity, light and wind). Special Materials and Equipment: Test plots and seeds of local crops. References: Hartman, H., Flocker, W., and Kofranek, A. PLANT SCIENCE, GROWTH DEVELOPMENT AND UTILIZATION OF CULTIVATED PLANTS. Evaluation: Quiz by instructor TOPIC PRESENTATION: CLIMATIC FACTORS AFFECTING PLANT GROWTH A. The distribution of 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 determines the configuration of the earths surface. b. Climatic patterns result from the circulation of the earth's atmosphere. B. Temperature 1. Plants of different species vary widely in their tolerance of temperature extremes. a. Some bacteria survive temperatures of 194 degree Fahrenheit. 2. The minimum and maximum temperatures to support plant growth generally are between 40 and 120 degrees Fahrenheit. 3. The temperature at which optimum growth occurs varies with the plant and differs with the stage of development. 4. Most plants require a lower night than day temperature. 5. Some plants require a cold season to complete their annual life cycle. 6. 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. C. Water 1. Water provides forces that maintain the organization of living cells. Dehydration kills chiefly because it disrupts this organization. 2. Water also serves as a medium for storing and transporting materials. Most of the materials made by plants can dissolve in water. 3. Plant growth is based on water uptake by cells. Most of the volume of young tissue is water. 4. Water is important in regulating Earth's temperature. a. Large bodies of water absorb much of the sun's heat without much increase in temperature, because the heat is spent in evaporating water. This is why seacoasts are cooler than inland areas in summer. b. When the air cools, water vapor condenses into droplets (fog, rain, or snow). This releases heat and limits the drop in temperature. Thus, seacoasts tend to be warmer in winter than dry inland areas. 5. High humidity may cause problems in agriculture because it promotes the growth of fungal disease organisms. 6. Precipitation (usually rainfall) provides most of the water for plants. a. An area receiving adequate rainfall during 2/3 of the growing season generally would have enough water for most crops. b. Rain for less than this amount of time would require some irrigation. c. The amount of irrigation needed depends on the nature of the plants, the temperature, and the amount of precipitation. D. Light 1. Plants use light as the source of energy for growth, through the process of photosynthesis. a. A few plants (example: dodder) lack photosynthesis and are parasites on other plants. b. Plants can live for a time in darkness, using stored foods. c. Light intensity (brightness) determines the amount of energy available for photosynthesis, so intensity influences the rate of growth. 1) Light intensity is often measured in units called foot-candles. 2) Sun-loving plants thrive on high intensities. Examples are corn, potatoes, and fruit trees. 3) Shade-loving plants do not grow well at high light intensities. Examples include many ferns and houseplants, as well as camellias. 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 the shade case 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 crops, 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 between 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. E. Air movement patterns in the atmosphere are the result of the suns' radiation striking more directly on the tropical regions (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 a crop at critical times such as bloom and pollination periods, or during early stages of leaf or fruit growth. __________________________________________________________ ACTIVITY: Have students do plot tests to observe the environmental effects of temperature, rainfall (irrigation), light, and air movement. __________________________________________________________ 7/20/90 sg #%&C