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Unit 5: Temperature & Light Chapters 8 & 9
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Unit 5: Temperature & Light Unit 5 Objectives: Identification of major cool/warm season crops Understand how temperature effects plants Use of growing degree days Discussion on the effect of light on plants Understanding of day length and photoperiod Awareness of light quality and intensity
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Unit 5: Temperature & Light Biological Temperature Range Plants vary in their ability to tolerate temp differences Each plant has a lower temp at which it cannot grow, a zone in which growth is optimized, and a upper temp limit in which growth will again stop Common crops can be divided into Cool- season and Warm-season categories Cool-season – survive mild spring frosts, may be planted early spring or in fall
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Unit 5: Temperature & Light Examples: Lettuce, Onions, Turnips, Cabbage Can you name some others? Warm-season – usually killed by frosts, require warmer temps to grow properly, planted later in spring Examples: Cotton, Peas, Peppers, Tomatoes Can you name the rest? Some plants have adapted to various temp ranges in order to survive
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Unit 5: Temperature & Light Others cannot survive at all Tropical plants, annuals Hardening Cool-season vegetables can be adapted to cooler temps by gradually exposing young plants to cooler temps Allow to wilt slightly before watering Grow at 10º below normal Plants become tougher, less likely to die from low levels of stress
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Unit 5: Temperature & Light Temperature and Dormancy Ex. Trees dropping their leaves, or wheat Bulbs and some weeds can be killed off to the ground but survive on the underground parts of the plant Also seeds are able to overwinter (the worst weeds are good at this) Most can only survive in dormancy to a certain lower temp Survivability may depend: Length of cold spell, wind, temp, age of plant, soil moisture
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Unit 5: Temperature & Light Spring warm spells followed by quick cold snap can be very deadly Not all parts of a plant can go dormant Ex. Flower buds on peach trees, cold kills flowers, but tree survives Seed Germination Temperature determining factor is seed germination Temp must be in the optimal zone for germination to occur Too cold or too hot will deter proper germination
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Unit 5: Temperature & Light Thermoperiod Daily temp range Maximum growth occurs when day temp is ~15º higher than night temp Allows the plant to photosynthesize and respire at optimal rate during the day, and rest at night Growth only occurs when photosynthesis is greater than respiration Otherwise the plant expends time breaking down extra energy Plants vary also is this manner Some prefer warmer or cooler night temps
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Unit 5: Temperature & Light Plants can be classified hardy or nonhardy depending on ability to withstand cold temps When might injury happen to nonhardy plants? Plants must still get water in the winter Why? What is occurring in the soil? Climatic Classification Can divide the U.S. into hardiness zones for plant growth (by USDA) Determines the types of plants that will grow based on the avg annual minimum temps
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Unit 5: Temperature & Light North America divided into 11 zones 1 coldest, 11 warmest Zones pretty much follow logic, but there are some variations Where might we find some exceptions? Not only hardiness zone must be taken into account, many other factors are still in play Soil types, rainfall, daytime temp, day length, wind, humidity, heat Ex. Phoenix and Portland are both in Zone 8 – can we grow the same plants?
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Unit 5: Temperature & Light Growers can use Hardiness Zones as a general guideline, but must have extensive local knowledge Growing Degree Days Used to estimate the growth and development of plants and insects during the growing season Concept: development will only occur if temp exceed a minimum threshold or base temp (Tbase) Base temps are determined for each organism & they’re all different
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Unit 5: Temperature & Light Calculating GDD Take avg of high and low temp for the day If that temp is at or below Tbase, GDD=0 If avg temp>Tbase then take that avg – Tbase = GDD Lets do some examples: High 47º, Low 32º Tbase for Wheat is 40º What is the GDD? High 75º, Low 55º What is GDD?
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Unit 5: Temperature & Light Modified GDD Similar to previous GDD, except upper temp never goes above 86º, and low never goes below 50º If temps are outside these parameters they are reset to that constant Used to monitor the development of corn Assumption is development is limited above 86º Use of GDD Growth and development of plants and cold- blooded animals depends on heat in and around them
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Unit 5: Temperature & Light Used to help monitor growth, and predict pest or disease risk After base temp is exceeded growth begins, but it slows/stops if temp falls below the base State of development correlated to the accumulation of daily GDD’s through the growing season This data is very accessible from agricultural weather stations and on the web Accuracy of the information is increasing as more data becomes available and relationships are established
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Unit 5: Temperature & Light A Crop Production Example Corn hybrid maturity ratings are related to temp effects Most widely used system in U.S. has two facets A corn plant must accumulate a certain amount of heat in order to complete its life cycle The total amount of heat needed will be relatively constant for a given hybrid Use GDD’s to calculate these maturities Tbase is 50º - corn makes little to no growth below this temp Max is 86º - growth rate declines to due excess respiration and moisture stress
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Unit 5: Temperature & Light Rate from planting to physiological maturity GDD’s can then be used as a decision-making tool Choose hybrid fitting the season based upon intended planting date to maximize season length Can make adjustments to seed selection if planting is delayed based upon the number of possible GDD’s May help schedule harvesting Not all seed companies use the same system, so ask if this is going to be a tool you use
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Unit 5: Temperature & Light Vernalization Promotion of flowering by forcing cold treatment to plants Exposing to warmer temps early and reversing the process called devernalization Ex. Tulip bulbs Forcing cell activity in the meristematic tissue
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Unit 5: Temperature & Light Temperature Stress Effects many essential growth processes, including biological reactions Reaction rates increase w/ temp Ex. Photosynthesis Absorption of minerals and water also affected by temp
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Unit 5: Temperature & Light High & Low Temp Injury Low temp usually results in frost injury What are our frost free dates in this area? Warm spells in the spring can stimulate early growth which can then be killed by cold High temp injury Often related to light and water effects May kill cell protoplasm
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Unit 5: Temperature & Light Nature of Light Form or radiant energy Travels in waves Distance between called wavelength Human eye sensitive to wavelength 400-700 nm Called white light Made up of red, orange, yellow, green, blue, violet Each color has different wavelength Which is longest/shortest? When light is trapped it becomes another form of energy Ex. – absorbed energy becomes heat
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Unit 5: Temperature & Light Photosynthetic organisms contain chlorophyll which is responsible for trapping light and converting it to chemical energy Plants appear green because chlorophyll reflects the green color Wavelengths absorbed by chlorophyll then called absorption spectrum Violet, red, and some blue are readily absorbed and changed to chemical energy
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Unit 5: Temperature & Light Sunlight Minimum duration of sunlight required for survival Light Quality & Intensity Most ag plants require >6 hrs or full sunlight/d to produce respectable yields Increased shade or clouds decreases yield and plant appearance Some plants have sun/shade preferences for optimal growth
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Unit 5: Temperature & Light Ex. Most garden plants prefer full sun, however leafing vegetables tolerate more shade Plant’s ability to move leaves to be parallel with a light source Movement called phototropism Light & Germination Shoot grows up away from gravity, root grows to gravity Response to gravity called geotropism Shoots begin to synthesize food as soon as they are exposed to light
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Unit 5: Temperature & Light Shoots will try to reach light until the food in the seed is used up Shoot will be white with no leaves until emergence Death occurs if food is depleted before emergence White stem w/ little leaf growth called etoliated Light Absorption & Photomorphogenesis Light absorption occurs like an antenna collects radio waves Radiant energy is collected and quickly transferred to processing Energy is processed to perform more chemical reactions, or synthesize plant nutrients
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Unit 5: Temperature & Light Light can be transferred in one-millionth of a one- millionth second Photosynthesis is unique because it can trap this energy very effectively and quickly stabilize it before it escapes in another form Photomorphogenesis is the process of converting these collected energy molecules and fixated carbon dioxide and converted into other molecules: proteins, fats, etc. Carbon dioxide fixation in the plant occurs w/ the enzyme ribulose phosphate carboxylase
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Unit 5: Temperature & Light As the amount of this enzyme increases, or works more efficiently, plant production is increased Photoperiodism Response to day length Example response to day length is flowering Plants can be divided into 3 categories based on their preferences for flowering initiation Long-day, Short-day, and Day-neutral Actual response is to amount of uninterrupted night
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Unit 5: Temperature & Light Flowering will not be affected by short periods of dark during the day Flowering will be inhibited by short periods of light during the night By understanding photoperiod needs, we can sometimes manipulate flowering in plants What are some plants that we might do this with? Long and short-day varieties of some plants have been developed to take advantage of different day lengths Example?
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Unit 5: Temperature & Light Artificial Illumination Looks the same, but quality varies Can be heavy to some colors of the spectrum May need to mix lights to maximize growth w/ artificial light Light Color & Plant Growth Light quality refers to color and wavelength reaching the plant surface Red & blue light best for plant growth Green light not beneficial because the plant reflects it
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Unit 5: Temperature & Light Red and blue light will encourage flowering Fluorescent lights are high in blue light and encourage leafy growth Good for starting seedlings Most commercial grow lights are fluorescent w/ a mixture of red and orange Incandescent lights are high in red and orange, but may be too hot Growing Plants Under Artificial Light Light most essential factor for indoor or greenhouse plant growth
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Unit 5: Temperature & Light Grow and time of activity depends on duration of light Three aspects to consider: Intensity Influences manufacture of plant food, stem length, leaf color, flowering Depends on proximity to the light source Windows can effect greatly due to which direction they face – southern exposures have most intense light, eastern/western have 40% less, northern have 80% less Duration Only key if the plant if photosensitive for flowering Or if you want to manipulate flowering
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Unit 5: Temperature & Light Low light intensity may be supplemented by increasing duration Illumination should not exceed 16 hrs Quality Must be considered when using artificial lights Select your light source carefully, and know what color light it produces and how that will affect the plant
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