herbaceous plants - 85-95% water
woody plants - 75-85% water
FUNCTIONS OF WATER
1) solvent - dissolves
2) reagent - water is used in biochemical reactions, such as photosynthesis.
3) translocation medium - water translocates solutes in xylem and phloem.
4) temperature relations - water is very
important in regulating temperature.
5) turgor pressure and growth
- the positive pressure inside of cells due
to water uptake.
growth - an irreversible increase in size or mass.
- shrinkage of individual cells due to
loss of turgor pressure that causes
- excessive water loss that causes loss
of plant rigidity;
|UNITS FOR EXPRESSING HUMIDITY
humidity - amount of water vapor in air; can be expressed as:
a) absolute humidity - amount of water vapor in air expressed as grams water per cubic
meter of air (g/m3)
b) specific humidity - amount of water vapor in air expressed as grams water per kilogram
of air (g/kg)
c) relative humidity - amount of water vapor in air expressed as a percentage of the amount
of water vapor that could be held at saturation.
d) vapor pressure - amount of water vapor in air expressed as the downward pressure
exerted by the water vapor present in the atmosphere. (1-55 mm Hg).
RELATIONSHIP BETWEEN HUMIDITY AND
TYPES OF CONDENSATION
TYPES OF PRECIPITATION
Edwards in Texas
Ogallala in Mid-West
sapwood - the lighter outer rings of wood through which all the water moves up the stems
heartwood - the inner darker rings that are clogged with resins, tannins, and other compound that resist
decay and supplies support.
absorption - uptake of water by roots.
movement of water through plants, mainly through xylem
guttation - loss
of liquid water from leaves;
SITE OF WATER ABSORPTION
2) older roots - little
absorption due to:
COHESION THEORY OF TRANSLOCATION IN THE
2) Causes negative pressure in leaves
3) Column of water is pulled up
in the xylem and translocated due to:
FUNCTIONS OF TRANSPIRATION
2) evaporative cooling of
leaves: 540 cal of heat energy is
dissipated for every gram
Transpiration is usually much greater than is needed to satisfy these two functions. Thus, many horticultural practices attempt to minimize excessive transpiration.
1) leaf area - smaller leaf area decreases transpiration, mesquite
2) leaf orientation - vertically orientated leaves decrease transpiration, yucca
4) stomata - when stomata are closed, transpiration decreases
3) light intensity
4) wind - as wind
increases, transpiration increases, but if the wind
gets too high, then the
5) soil water
TECHNIQUES USED TO DECREASE
2) decrease light intensity - grow plants under shade
3) harden-off seedlings
4) antitranspirants -
chemicals that close or clog stomata.