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ENVIRONMENTAL FACTOR: temperature
a) low temp. decreases transpiration
b) high temp. increases transpiration, but when it gets too hot the stomata close, then transpiration may decrease
ENVIRONMENTAL FACTOR: light intensity
a)darkness decreases, b/c stomata close (except for CAM plants open at night)
b) high light intensity increases temp. which increases transpiration, until stomata close then transpiration may decrease; occurs midday during heat of summer.
ENVIRONMENTAL FACTOR: wind
as wind increases transpiration increases, but if it gets too windy, stomata may close and transpiration may decrease.
ENVIRONMENTAL FACTOR: soil water
a) when soil is moist, transpiration occurs according to the above factors
b) when soil is too dry, stomata close causing transpiration to decrease (overrides above factors)
DECREASE TRANSPIRATION: mist or spray foilage
a) in propagation an intermittent mist system is used
b) mid-afternoon sprinkler irrigate plants in greenhouses/nurseries
DECREASE TRANSPIRATION: harden off seedlings
a) decrease watering
b) decrease temperature
c) decrease fertilizer, especially N.
DECREASE TRANSPIRATION: antitraspirants
chemicals that close or clog stomata
a) physiologically cause stomatal closure
b) wax, resin or latex that clogs stomata
the substrate in which plants grow. Usually appied to manufactured or synthetic soils.. EX: "potting soild", or highly amended soils (landscape beds)
Functions of soil or growing medium
1. Support and anchorage
2. Supplies mineral nutrients
3. Supplies water
4. Allows gas exchange- especially O2 and CO2, but also ethylene
A Horizon or topsoil
-abundant life, therefore, high in organic matter
a compacted, impermeable layer in the A horizon due to repeated plowing or tilling (approx. 6 inches deep)
B Horizon or subsoil
-less weathered; higher in clay
- less life, therefore, low in organic matter
C Horizon or parent material
-little life, except deep rooted plants and little to no organic matter
-loss of liquid water from leaves
- occurs through hydathodes (similar to stomata, but they do not close)
Cohesion Theory of Translocation in the Xylem
1) Transpiration occurs and is driving force
2) Causes negative pressure in leaves
3) Column of water is pulled up in the xylem and translocated
driving force for translocation
transpiration causes a negative pressure in leaves, which "pulls" the water up the xylem
evaporative coling of leaves
540 cal of heat energy is dissipated for every gram of water that evaporates from leaves, which is a major contributor to the cooling of leaves
4 Major Components (in a well watered, but well drained loam soild)
air, water, mineral particles, organic matter
relatively inert; results in:
a) a little effect on soil chemistry and pH
b) poor nutrient holding capacity (CEC)
b)wet: viscous and gelantinous; sticky--dry: hard, packed and cohesive
c) Micelles: laminated into stacks
d) very large surface area
e) very small pores
BASIC: saline-sodic soil
pH 8-8.5, greater than 2,000 ppm total soluble salts and 15% or more of CEC occupied by Na
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