Transcript plants day 5

PLANTS DAY 5
FACTORS THAT AFFECT PLANT GROWTH
SUNLIGHT
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Quantity and quality of light
influence a plant’s ability to
perform photosynthesis
Quantity limited by natural
environmental factors like
latitude and competition
from taller plants
Quality of light is influenced
by shading by other plants,
cloud cover, time of day, and
angles of incidence during
different seasons – duration
of natural light is dictated by
the seasons
TROPICAL
RAIN FOREST –
LOTS OF
SUNLIGHT
YEAR ROUND
TEMPERATE RAIN
FOREST (B.C.)
LOTS OF SUNLIGHT
FROM MAY SEPTEMBER
Each m2 of
ground
absorbs only
66% of solar
energy
Each m2 of
ground
absorbs
100% solar
energy
SUNLIGHT
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Photoperiod, number of daylight hours in a 24 h
period, is variable the further away from the
equator plants are
Northern hemisphere = longer daylight hours in
spring and shorter daylight hours in fall and this
affects productivity and reproductive life cycle of
plants
Different plants react differently to photoperiod
length
SUNLIGHT
• Latitudinal variation in the intensity of
sunlight results from the Earth's spherical
shape; seasonal variation in solar radiation in
the Northern and Southern Hemispheres are
due to the Earth's tilt of 23.5º relative to its
plane of orbit.
• Only the tropics receive sunlight from
directly overhead year round
• The tropics receive the greatest annual input
of solar radiation and show the least seasonal
variation; only small variations in daylength
and temperature occur.
• Seasonal variation in light and temperature
increases steadily toward the poles
PHOTOPERIOD
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Photoperiod changes dramatically during the year in temperate regions of the world.
For many floriculture crops, photoperiod controls growth and flowering, and a small
change in photoperiod can mean the difference between vegetative growth and
rapid flowering
Short-day plants are those that flower, or flower more rapidly, when the photoperiod
is shorter
Long-day plants are those that flower, or flower more rapidly, when the photoperiod
is longer
For example, poinsettias and chrysanthemums develop vegetative growth when the
photoperiod is long and flowers when the photoperiod is shorter.
Growers use blackcloth to provide short days to induce flowering of poinsettias
By knowing how daylength affects plant development in photoperiodic species, we
can manipulate the natural photoperiod to promote vegetative growth (such as to
bulk up plant size or for cutting production) or flowering, whichever is desired.
Therefore, successful production of many crops requires an understanding of how
plants respond to photoperiod, how photoperiod changes during the year and how to
modify the photoperiod to control growth and development.
WATER
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Water is a part of photosynthesis; maintains turgor
pressure/firmness of plant tissue and transports
nutrients throughout the plant
Amount of water regulates opening and closing of
stomata = regulates transpiration
Is a solvent for minerals moving into the plant
(osmosis) and for glucose to move to their site of
use/storage (translocation)
HUMIDITY
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Relative = water in air
Humidity water air could hold at a given temp.
Warm air holds more water vapour than cold air
Similar to process of diffusion, water vapour will move
from areas of high humidity to areas of low humidity
Humidity in air space between cells in plants is almost
100%, so when stomata are open, water vapour rushed
out into air that is less humid
As water vapour rushed out, cloud of high humidity
forms around stomata and this slows down transpiration
and helps to cool the leaf = stomata closes tighter so as
not to let as much water out
NUTRITION
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Macronutrients: The nutrients that are required by
plants in larger quantities are termed as the
macronutrients.
Micronutrients: The nutrients that are required in
smaller quantities by the plants are called as the
micronutrients.
The eight micronutrients include iron, zinc,
molybdenum, manganese, boron, copper, cobalt,
and chlorine
Macronutrient
Nitrogen
Potassium
phosphorus
Calcium
Magnesium
sulfur
Functions
Makes up amino acids and thus all
proteins and nucleic acids and
chlorophyll
Leaf growth
Involved in water balance to control
operation of stomata and water
intake in roots; needed to help make
proteins
Component of DNA, RNA; needed for
mitosis and cell division
Important in developing and
functioning of cell walls
Component of chlorophyll
Component of most proteins
ACIDITY
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Acidity is measured in pH
level, a chemical property
that governs how substances
interact with each other
A wide range of natural
acidic properties are
present in soils, but some
soils may become too acidic
for plants to grow healthily
They can be treated with
alkaline (basic) substances
to make them more acidneutral.
ACIDITY
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The acidity inhibits the growth of roots and the absorption
of necessary minerals through the root cell walls = weaken
plants, causing them to grow very slowly or turn yellowish in
color = if acid remains high, plants may wither and die
Different plants can survive in different acidity ranges, and
hardier plants will be able to deal with high acid levels
more easily.
Areas with heavy rainfall tend to have more acidic soil,
simply because the rain water leeches away alkaline
minerals in the soil
Soil with high levels of limestone will be more alkaline,
while soils with high levels of granite, biomaterial (compost),
peat moss or man made acidic fertilizers tend to be more
acidic
PLANTS AND ACIDITY
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Plants that thrive in acidic soil: blueberry, gardenia,
azalea
Plants that thrive in alkaline soil: broccoli,
muskmelon, onions
TROPISM
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Plants grow in response to external stimuli; growth
responses are called tropisms and are controlled by
plant hormones
Positive tropisms are growths towards stimulus
Negative tropisms are growths away from the stimulus
Phototropism: bending and growth of a stem towards
a light source – capture more sunlight energy
Gravitropism: growth response to gravity. Stems show
negative gravitropism and roots show positive
gravitropism
Thigmotropism: growth in response to touch – vines
gain support by growing around a stem or tree trunk