Download Unit 5: Temperature & Light

Unit 5: Temperature &
Light
Chapters 8 & 9
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
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 Coolseason and Warm-season categories
 Cool-season – survive mild spring frosts, may be
planted early spring or in fall
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
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
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
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
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
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
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?
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
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?
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 coldblooded animals depends on heat in and around
them
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
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
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
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
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
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
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
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
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
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
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
Unit 5: Temperature & Light
 Light can be transferred in one-millionth of a onemillionth 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
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
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?
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
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
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
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