Light & Water Flashcards
Radiation that strikes on an object does three things
reflects off and back
absorption
transmission
Greenhouse effect
Transmission of radiation through glass/atmosphere Shorter wavelengths only absorbed Objects in greenhouse heat up Objects re-radiate as heat long wavelengths only Long waves cannot get back out through
Light’s Characteristics
spectral quality (color or wavelength)
intensity (# of photons, amt. of energy)
duration (length of light period)
direction (angle of incidence)
Spectral quality
380 violet 430 blue 500 green 560 yellow 600 orange 650 - 760 red
Photosynthesis (pertaining to light)
Only red and blue light is absorbed by chlorophyll and other pigments
The absorbed part of the spectrum is called PAR
Photosynthetically Active Radiation
Light Intensity (Quantity)
intensity is measured as micromoles/square meter/second
sunlight ranges between 1000-2000
interior light can range as low as 50
Compensation point
at a certain light intensity, a plant captures as much energy through photosynthesis as it needs to survive
photosynthesis = respiration
at this point, the plant will neither die nor grow
below CP, a plant will die
above CP, a plant will grow
Saturation Point
at a certain light intensity, a plant captures the maximum amount of energy through photosynthesis that it is able to do
At lower light intensities, a plant will respond to brighter light (grow faster)
Above the SP, brighter light has no effect on growth rate
Compensation Point & Saturation Point (comparing shade and sun plants)
Sun-loving plant species tend to have a higher saturation point
Shade-loving species tend to have a lower compensation point
Duration
plant growth rate and productivity is dependent on
- how much time the plant receives PAR above the Compensation Point
- how far above the CP it is
Horticultural Practices with Light
spacing - light exposure
pruning - allow light penetration into tree or shrub canopy
eliminate weeds that compete for light
supplemental lighting
Advances of supplemental lighting
increase intensity
increase duration
Supplemental Lighting
Incandescent vs. Fluorescent
Supplemental inefficient short life span high in red portion Fluorescent efficient expensive high in blue
HID
High Intensity Discharge lamps -metal halide, sodium vapor -most efficient -spectral composition varies metal halide - green/blue sodium - red/orange
LED
Light Emitting Diode lamps
- precise control of spectral composition, can change to match to plant needs, life cycle
- cool
- very efficient
- very long life span, low maintenance and disposal cost
Other plant processes/ light
photoperiodism - LD vs. SD
seed dormancy - some seeds need light to germinate
branching & stem elongation
-both involve red vs. far red light
Red / Far Red Light
much of red is absorbed
much of far red is transmitted
Branching / stem elongation
sun - red:far red ration is balanced
shade - far red > red
red promotes short internodes, more branching in full sun
far red promotes less branching, longer internodes in the shade (“stretching” and more “open” plant for)
What does water do in a plant
a solvent for chemical reactions substrate for chemical reactions carrier for mineral uptake provides turgidity - maintains plant form and is a driving force for growth provides cooling via evaporation reduces rapid temperature change
Water in soil
water is found in spaces between soil particles
when spaces are full of only water (no air) the soil is saturated
water drains out of soil due to gravity
The water soil holds after gravity is called
field capacity
larger pore capacity is filled with air, and the smaller spaces are filled with water
Water removal from soil
evaporation
transpiration
through plant and incorporation into growth
Factors influencing transpirational water loss by a plant
environmental
- temp
- humidity (higher humid, less water loss)
- wind
- light
plant properties
- leaf area, shape/form leaf
- stomata: density, size
- cuticle thickness and composition
- leaf surface: color, waxes, hairs, trichomes
- leaf exposure: aspect to sun, leaf curling
When water is in short supply
at field capacity, water that a plant can use is called: available water
when all water is gone, there is still some water in soil, but it is held by the soil structure too tightly for plants to get; that stage is called the permanent wilting point
At a time when transpirational water loss is greater than water absorption
stomata close biochemical changes in plant cells reduced growth and productivity leaf rolling and wilting recovery if water is restored, or if severe enough, permanent wilting and plant death
Supplemental water
types of irrigation
flood or furrow supply canal field canal sprinkler pipe/risers/valve nursery overhead irrigation water gun greenhouse auto-irrigation
low volume
trickle, drip
capillary mat
Issue: Water Use Efficiency, Nutrient Pollution, Recycling
Environmental concerns over wetlands preservation, pollution, etc. are changing horticulture so that more efficient water use, recapture and recycling of water are becoming more commonly used and eventually will be required by law
Determining when to irrigate
aerial imaging - satellite/airplane
in soil devices - tensiometer, gypsum block, neutron probe, electrical conductivity meter
weather data (temp/precip./evap.)
