Download Translocation and Transpiration

Translocation and
Transpiration
Horticulture
Plant processes
1. What is the role of water in
plants?
• It is a necessary constituent of all
living plant cells and tissues.
• It serves as a medium for dissolved
nutrients and minerals from the soil
and takes them to production or
storage to sites where they will be
used.
• In plants, water is a needed to carry
out many metabolic processes,
including photosynthesis.
• water acts as a coolant and
temperature buffer.
Types of WATER FOR PLANTS
• Moisture for plant growth is stored in the soil.
– An average of about 500 pounds of water is
required to produce one pound of dry plant
material.
– About 5 pounds, or 1 %, of this water
becomes an part of the plant.
– The remainder, the other 495 lbs, is lost
through the stomata of the leaves in the
course of transpiration.
Types of water
• Capillary water is used by the plants.
– This water moves freely in the soil and
can move up and down, or horizontally.
• Forms of soil water not available to plants
include
– gravity water, which is lost to
drainage,
– hygroscopic water that bonds to the
soil particles
Translocation
• Water moves through the plant by translocation
and transpiration.
• Water moves through the Xylem and Phloem
• Roots have no other means to nourish
themselves, and would die without translocated
sugars manufactured in the leaves.
Translocation
• translocated water adds turgor or stiffness
to the cells.
– This pressure helps to provide support to
leaves and new tissue.
• Translocated water also enables a plant
to:
– Maintain temp
– to carry on most chemical reactions,
– to maintain the volume of the cytoplasm
Transpiration
• Transpiration is the
evaporation of water
from leaf and plant
surfaces.
• It is the last step in a
continuous water
pathway that starts
from the soil and
ends in the
atmosphere.
• Respiration and Transpiration
produce heat
• Transpiration cools the plant.
–About 90% of all water that enters
the plants from the roots is given off
during transpiration.
–The other 10% becomes involved in
chemical processes or is tied up in
the plant's structure.
Stomata
• The lower surface of the leaf is dotted with special porelike structures called "stomata."
• “Guard cells”
– Open during the day to permit gas and water vapor
exchange with the atmosphere.
– Close at night or when the plant is under stress.
Stomata
• Water loss is directly proportional to
the surface area exposed to air.
– Most of the surface area of a
growing plant is leaf area.
• Desert plants frequently have very
small leaves or even thorns in place
of leaves.
– They may also have fleshy
stems that store water. Fleshy
stems and thorns, or very small
leaves, are adaptations that help
plants survive in hot, dry
climates.
• http://search.msn.com/images/results.aspx
?q=transpiration#focal=15b6b2d3f3c02fb0
8a22aa33b0e0eaaf&furl=http%3A%2F%2
Ftechalive.mtu.edu%2Fmeec%2Fmodule0
1%2Fimages%2Ftranspiration.jpg
Wilt
• Water is taken up by root hairs
• When they lose water more
rapidly than they take it up, they
wilt.
• When this occurs, life processes
slow and growth may even stop.
•
If a plant remains wilted for too
long, it will be damaged and may
die.
– include yellowing, leaf drop
and stunting.
– These usually result in yield
loss and less profit for the
producer.
Water stress
• Water stress is more important to
plants at certain times.
– Germinating seed can be killed
very quickly by lack of water.
– Lack of water will also cause
many plants to drop flower
buds, flowers or even small
fruit.
– Pollen may not develop fully if
plants lack water.
• Corn, for example, may
have many missing grains
on the ears if adequate
water is not available during
pollination.
Indications of water stress
• Show before permanent damage is done
– Leaves develop a greenish blue tint and may
wilt or roll (corn).
– Pumpkins and other plants with large leaves
often wilt during the day and recover at night.
When they remain wilted overnight, they need
water immediately to prevent yield reduction.
Too much moisture
• can be just as bad as too little moisture.
• seeds and plants also require oxygen and
carbon dioxide to germinate and grow.
• Seeds and the roots of plants in waterlogged soil
may not receive the gases they need to maintain
life processes.
• Roots die, diseases set in, and both roots and
seed may rot.
– Plants yellow and become stunted.
– Even large trees can be killed by having their roots
covered by water for too long.
EVAPOTRANSPIRATION
• Evapotranspiration (ET) is the total amount of water
removed from soils by evaporation and plant
transpiration.
• Soil evaporation is a direct pathway for water to move
from soil to the atmosphere as water vapor.
• Over the course of an irrigation season, soil evaporation
is 20% to 30% of total ET.
• Soil evaporation rates are highest after irrigation or
rainfall.
ET
• Evapotranspiration can be affected by the
– weather,
– the crop type,
– the crop growth stage,
– the crop variety,
– the crop population,
– surface cover and tillage,
– the availability of soil water.
Factors affecting
• Weather factors that have a major impact on this
evaporative power include:
–
–
–
–
air temperature,
humidity,
solar radiation
wind.
• Different crops use different amounts of water
over the course of the growing season.
– corn in the Midwest requires 23 to 28 inches of water
in a season; winter wheat requires 16 to 18 inches;
while alfalfa requires 31 to 36 inches.
• . Demonstrate the amount of water in
various fresh plants. Collect samples of
fresh plants or plant parts. Keep them in a
plastic bag until they can be weighed.
Weigh about 100 grams of a sample and
then dry it in an oven at 100 F, or use a
microwave to dry the samples. Weigh the
dry samples and determine the amount of
water in the plants and report your results.