1. Unit 5: Temperature & Light Chapters 8 & 9

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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?

11. 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

12. 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?

13. 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

14. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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

27. 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

28. 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?

29. 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

30. 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

31. 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

32. 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