temperature - a qualitative measure of the amount of heat energy;
- it is a measure of the intensity or degree of heat energy.
heat - a quantitative
measure of the amount of heat energy;
kilocalorie (kcal) - 1,000 calories
British Thermal Unit (BTU) - amount of heat required to raise 1 lb. of water by 1 oF.
specific heat - amount of heat (# calories) needed to raise 1 g of a substance by 1 oC. (water = 1.0)
heat of fusion - amount of heat
(# calories) needed to change 1 g of a substance from
heat of vaporization - amount of heat
(# calories) needed to change 1 g of a substance from
WAYS TO TRANSFER HEAT (HEAT ENERGY)
There are 3 ways in which heat (heat energy) can be moved.
1) conduction- flow of heat energy through a medium from molecule to molecule.
2) convection - mass movement of heat energy.
3) radiation- flow of
energy as electromagnetic waves, with no transferring
the Greenhouse Effect Happens
Dioxide Emissions and Global Warming
|1) specific heat
- stabilizes the temperature of plants (plants are 75-95% water)
- stabilizes the temperature of the environment, esp. around large bodies of water (coldest temperature US)
2) heat of fusion
3) heat of vaporization
4) infrared (IR) radiation
5) change of state
|Climate - the average
atmospheric conditions over a long period of time.
Weather - the current and temporary atmospheric conditions.
TERMINOLOGY USED TO DESCRIBE CLIMATE
OVER SMALL AREAS
2) Temperate Climatic Zone
a) sub-tropical -
often used to describe the southern most area of the
Temperate Climatic Zone
3) Arctic Climatic Zone
THE POSITION OF THE EARTH RELATIVE TO THE SUN
(also determines photoperiod and day length)
|The earth's axis is tilted 23 1/2 degrees
relative to the axis of the sun. As the earth
revolves around the sun, the axis remains pointed in
the same direction in space. Notice:
The earth's axis is orientated 23 1/2 degrees towards the sun, thus the sun's rays strike the earth at a 90 degree angle at the Tropic of Cancer.
The situation is reversed, i.e. the earth's axis is orientated 23 1/2 degrees away from sun, thus the sun's rays strike the earth at a 90 degree angle at the Tropic of Capricorn.
The earth's axis is neither orientated away from nor towards the sun (I made up the term obliquely parallel to describe this, or sometimes I call it cock-eyed parallel), thus the sun's rays strike the earth at a 90 degree angle at the equator.
|1) Latitude - average
temperature decreases north and south from equator
Due to: (see
2) Time of Year or Seasonal Variation - temperature fluctuates most in the Temperate Zone
summer solstice - June 21 or 22, when earth's axis is tilted 23 1/2o towards sun.
Warmer due to:
a) sun's rays concentrated over smaller area
b) sun's rays travel through thinner layer of atmosphere
c) days longer
winter solstice -
Dec. 21 or 22, when earth's axis is tilted 23 1/2o
away from sun
vernal or spring equinox
- March 20 or 21, when earth's axis is oriented
autumnal or fall equinox
- Sept. 22 or 23, when earth's axis is oriented
a) minimum average temperature: around sunrise
b) maximum average temperature: mid to late afternoon
4) Time of Year -
hottest late summer
5) Elevation or Altitude
a) small scale - hot air rises, cold air sinks into low areas
b) large scale - the temperature decreases 0.6 oC/100 m or 1 oF/330 ft increase in altitude
6) Slopes - warmest to coldest slopes of a hill or side of a building: south > west > east > north
7) Water Bodies - stabilizes temperature; warmer in winter, cooler in summer
a) dark soils warm faster than light soils in spring
b) dry soils warm faster than moist soils in spring
Cardinal Temperature - the temperature range in which plants grow and survive.
Cardinal Temperature - Graphic Thermometers
Courtesy of Elle Herberger, spring 2023
Courtesy of Maya Rubio, fall 2020
MINIMUM CARDINAL TEMPERATURE
1) tender or chilling sensitive: 32 to 45 oF (0 to 7 oC)
2) semi-hardy plants: 15 to 29 oF (-9 to -2 oC)
3) hardy plants:
less than 0 oF (-18 oC)
1) in southern U.S.: grow as fall-winter crops.
2) in northern U.S.: grow in late spring, summer, early fall
b) warm season plants: grow best at 78-90 oF (24-32 oC)
1) in southern U.S.: grow in late spring and summer, early fall
2) in northern U.S.: grow in summer, but for
some warm season crops the growing season
MAXIMUM CARDINAL TEMPERATURE
b) survival: 130 oF (54 oC), most species.
|HOW HIGH TEMPERATURE DAMAGES PLANTS
A) Dies quickly
1) Denatures proteins (unfolding of proteins) - at 130 oF
B) Dies slowly or just poor growth
1) Desiccation - causes excessive drying-out
2) Sun scald or scorch - desiccation followed by death of tissue
3) Respiration exceeds
photosynthesis - depletes stored food
METHODS USED TO DECREASE HIGH
1) mulch - insulates and blocks out light
B) Air temperatures
1) Decrease light intensity (decrease both visible and infrared if possible)
a) lath house - wooden slates covering over nursery crops
b) shade cloth or saran over nursery crops or greenhouses
c) shading compound or whitewash painted on greenhouse roof
d) fluid roof greenhouse - colored solution flowing through a double-layered roof (not common)
2) Evaporative cooling (relies on heat of vaporization)
a) spray foliage and physical structures during mid-afternoon
b) fine mist or fog injected into a greenhouse
|TWO TYPES OF COLD TEMPERATURE INJURY
Chilling Injury - damage or death due to cold, yet above freezing temperatures (32 to 45 oF).
Freeze Injury -
damage or death due to temperatures below freezing
(below about 28 oF).
TWO TYPES OF FREEZES BASED ON HOW THEY OCCUR
1) Radiational Freeze or Frost
- temperature drops due to radiational cooling
2 Types of Radiational Freezes
white frost -
occurs when the temperature drops below both the
current dew point (dew forms)
frost - occurs when the
temperature drops below freezing, but remains
up during the day because the amount of visible and
infrared (IR) radiation from sunlight exceeds the amount
of long wavelength infrared radiation (IR) re-radiated
and lost from the earth's surface. Therefore, the
earth's surface warms up, which in turn warms up the air
next to the earth, thus the air temperature increases
close to the earth's surface.
surface slowly looses heat by re-radiating long
wavelength infrared (IR) radiation, thus the solid
objects of the earth's surface cool. This in turn
decreases the air temperature next to the earth's
surface. If enough energy is lost to drop the
temperature below freezing, a frost occurs. Thus,
a freezing layer of air occurs next to the earth's
surface with a warmer layer of air just above it (about
10-15 feet), which results in the development of a
The conditions for this to occur are: a) night, b) no wind, and c) no cloud cover.
|HOW CHILLING TEMPERATURES INJURE PLANTS
1) Increased protein and enzyme breakdown.
2) Increased membrane leakiness
a) membranes lose selective permeability
b) often appears deeper green and slightly waterlogged
Sensitive Plants: usually will not kill the plant, but may stunt its growth or damage parts of the plant.
1) Direct cellular damage - damage to individual cells.
a) Very rapid temperature
b) Moderate temperature drop
young tissue vs. old mature tissue
growing tissue vs. dormant tissue
flower buds vs. vegetative buds
roots vs. shoots
3) Frost heaving - soil freezes and expands, thus heaving the plant out of the soil.
4) Bark splitting - cambium under bark freezes, expands, then splits the bark.
5) Physical or mechanical breakage (ice damage) - from weight of ice on plant.
6) Sun scald or Southwest
injury - excessive desiccation
on southwest side of tree;
|HOW TO PREVENT A RADIATIONAL FREEZE OR
1) Decrease rate of radiational cooling
a) hot caps or plastic tents or blankets
d) fog or water vapor
e) smoke - oil burners or smudge pots
2) Increase air temperature
2) Radiational freeze methods
- some are moderately effective for mild,
4) Delay development in spring
- avoids damage to new spring growth and flower
5) Harden-off or cold acclimation in
fall: is a normal part of dormancy and
Allow to occur
naturally by observing the following:
|Dormancy- a state of
Purpose - to survive
TWO TYPES OF DORMANCY
a) Unfavorable environmental conditions
b) External factor, such as hard seed coat
How to overcome?
a) short days (SD)
b) decreasing temperatures
How to overcome?
chilling requirement - the number of hours of cold between 32-45 oF (0-7 oC) required to satisfy rest.
|Rest is very common amongst temperate perennial plants, which are perennial plants that are
native to the Temperate Climatic Zone. Rest is a
mechanism the plant uses to go dormant starting in the
fall in order to survive the cold of winter.
Rest also assures flowering, vegetative growth and/or
seed germination at the proper time in the
spring. The initiation of fall color is a sign
of plants going into rest, and the emergence of
flowers on fruit trees in the spring is a sign of
plants coming out of rest. It is the cold of
winter that satisfies rest. If a plant that is
in rest is not exposed to the proper amount of cold,
it may grow abnormally in the spring and/or may
eventually die. That is why we do not grow any
of our native temperate trees as indoor plants,
instead we use tropical trees that do not need cold to
VEGETATIVE AND FLOWER BUD DORMANCY
Cold is required for some trees and shrubs to flower and/or start vegetative growth in the spring, especially temperate trees, shrubs and other perennial plants that are native to the Temperate Climatic Zone.
Cold is required for some bulb crops to flower; especially bulbs native to the northern part of the Temperate Climatic Zone, for example tulip.
SEED REST OR EMBRYO REST
Cold is required for some seeds to germinate, especially seeds of trees and shrubs which are native to the Temperate Climatic Zone.
The chilling hour requirement of fruit trees must be matched to the chilling hour zone where the tree is to be grown. Your local county agent should be able to give you a list of cultivars that are adapted to your chilling hour zone. Reputable nurseries should only sell fruit tree cultivars adapted to your region. Below are the chilling hour requirements of selected cultivars of various fruit trees.
(From: G.R. McEachern. 1990. Growing Fruits, Berries and Nuts: Southwest-Southeast,
Gulf Publishing Co., Houston, TX)
|Biennial - plants that
have a 2 year life cycle.
exposure (1 day to 1 week) to high temperatures (90-95