Pioneers in A New Language
Martha Carlson, Sept. 2011
What did the sugar maple
tell the alien?
After a long discussion of its internal biochemistry,
the positive and negative aspects of its site, the
changeability of weather, and recent changes in
climate and atmospheric chemistry, the tree tipped
its leaves and reflected a few photons of near
infrared light towards something on the ground.
The alien turned to notice a small animated
creature that was vibrating with excitement.
The alien smiled and bent down to look at the
creature. The thin tissues that projected from the
alien’s skin flickered with blue, green and red light.
This lecture was developed for Monitoring Forest
Health, an upper level college course in the Dept. of
Natural Resources, College of Life Sciences, UNH.
Carlson taught this in Fall 2011 with Dr. Barrett N.
Rock. This power point explores pioneer work in
understanding the role of light in photosynthesis.
This lecture is presented on the Forest Watch website
for teachers and, with help from their teachers, for
upper level high school students.
“What is it? It
doesn’t reply,”
the alien asked
with surprise.
“That’s a human. They don’t have very
good receptors. They don’t light. They’re
ilphotonic.,” the maple reflected.
(By the end of this lecture, you will be able to define “ilphotonic”.)
Gates et al.
1965
What is the relationship between light and
plants? What makes plants grow? Heat? Light?
“…the interaction of radiant energy with the
plant leaf…”
Shull, 1929, McNicolas, 1931, Rabideau, 1946—Step by step, scientists
began unraveling the mystery. Dr. David M. Gates, a biologist at the
National Bureau of Standards at the University of Colorado, experimented
with spectroscopy and microscopy to find the answers.
Gates measured the size of cells in leaves(15 microns x 15 microns x 60
microns), counting the chloroplasts—he counted 50 inside one palisade
cell.
Gates’ New Concepts
• The Energy Environment!
“The energy absorbed selectively at
certain wavelengths by chlorophyll
will be converted into heat or
fluorescence, and converted
photochemically into stored energy in
the form of organic compounds
through photosynthesis.”
Anatomical Ideas
• The cells of the leaf are designed to
receive maximum light.
• The anatomical structures respond to
light as in:
Stomatal openings seemed to be connected
to light. And leaves absorbed light along a
light “action spectra”.
Gates Noticed Differences
Among Plants
Cactus—Reflect more
Lichens—Wet and dry
Conifers—Design of needles, holding
heat?
In Visible Light
Different reflectance and absorption
of light with different:
•
•
•
•
•
Angles
Wetness or Dryness
Age of Leaf
Pigments
Species
Different Wavelengths
• Green is Different
• Red is Different, changing as leaf grows
• Discovers the Red Edge Inflection Point.
• The REIP changes with growing leaf as
more chlorophyll is developed.
Near Infrared Light
• Differences in NIR reflectance might
be a function of cell shape, size and
amount of intercellular space.
• Thicker leaves have greater
reflectance.
• Why is NIR so reflectant? (Gates
doesn’t know about porphyrin ring
size and photon lengths).
Other Unanswered Questions
Heat energy and light energy. Measuring
both. Not sure about how the
photosynthesis systems dump heat.
Fluorescence at a slightly longer
wavelength—how does it work?
Photons Are Fast
and Very Small
Mini-Lesson before we proceed:
There are more femtoseconds in 1 second than there are seconds in 30 million years!
1 year= 31,536,000 sec. so 30,000,000 x 31,536,000 =9.4608 x
seconds in 30 million years!
th
1/1,000,000,000,000,000 ,
-15
1/10
14
10
or 946,080,000,000,000
part of one second in which a photon is absorbed!
Femtosecond.
1 billion = 1,000,000,000 1 million = 1,000,000
Time:
Femtosecond 10-15
billion millionths
-12
Pico second 10
million millionths
-9
Nano second 10
billionths
Microsecond 10-6
millionths
-3
Millisecond 10
thousands
One second 1
1
Reading Spectral Analyses
NIR 1
REIP
NIR3
Sample VIRIS, September 15, 2008
90
Leaf
Pigments
Tree 835
Tree 812
80
70
20
NIR, TM5
NIR, TM4
30
Red Light, TM3
40
Green Light, TM2
50
Blue Light, TM1
Percent Reflectance
60
Water
10
0
400
600
Blue Green Red
Visible Light
800
1000
Near Infrared
Light
1200
1400
1600
Wavelength (nm)
1800
2000
2200
2400
NIR 1
REIP
NIR3
Sample VIRIS, September 15, 2008
90
Leaf
Pigments
Tree 835
Tree 812
80
70
20
NIR, TM5
NIR, TM4
30
Red Light, TM3
40
Green Light, TM2
50
Blue Light, TM1
Percent Reflectance
60
Water
10
0
400
600
Blue Green Red
Visible Light
800
1000
Near Infrared
Light
1200
1400
1600
Wavelength (nm)
1800
2000
2200
2400
What are Nanometers?
Micrometer one-millionth of a meter,
6
10
9
Nanometer one-billionth of a meter, 10
Gates calls it a milli micrometer.
So to change 1.65 micrometers to 1650
nanometers, MOVE DECIMAL 3 spaces.
Rock et al., Remote Detection of Forest
Damage, 1986
Purpose of Research: “This…may allow scientists
to discriminate and identify unique spectral
signatures associated with the response of
vegetation to various stress agents…spectral
‘fingerprints’ associated with specific causal
agents of forest damage and decline.”
Dr. Barrett Rock is the founder of Forest Watch. He is a professor of
Natural Resources at the University of New Hampshire.
New Concepts
• Remote sensing can “see” the forest.
• What Thematic Mapper, aboard Landsat
satellite, 500 miles above Earth, sees can be
the same as leaf reflectances in the lab.
• Stress changes the absorption and
reflectances of light.
• Those changes in light disclose changes in
anatomy and pigments
Visible Light
Confident about what blue, green and red light
show.
The red edge “is directly correlated with leaf
chlorophyll concentrations”.
The REIP changes with health and with normal
senescence.
Concentrations of pigments will vary according
to stress.
Infrared Light
• NIR tells about leaf health, refractions along
cell-wall-water-air interfaces.
• Stress leads to less reflectance in NIR plateau.
• Water content may be seen in SWIR area.
Sensing Tools
Some spectrometers cannot detect enough
detail to see the blue shift in the REIP.
Satellite imagery can be displayed in “false
color composites.”
What Do We Know Now
Why does a leaf reflect NIR—porphyrins, photons are too
long and slow waves.
Fluorescence—a non-photochemical quenching of light
energy—photoinhibition --not energy dependent (as
carotenoids dump heat) and not a state transition (as
antenna detach). Indication of activity in chlorophyll.
Still mulling over the differences between temperature and
light energy. See Morton (my body produces 3x its weight in
ATP on an average day!)
Today we are inside those chloroplasts and know that there
are 600 million chlorophyll molecules in each chloroplast. In
one square cm of grass, you would have more than 30
million chloroplasts!
A single palisade cell with chloroplasts
(Photosynthesis.com).
What Do We Know Now
• More information about structure of
PSII and PSI and how they respond to
stresses and how they are damaged
by stress.
• Rock’s “water stress index”
recognized as TM5/4.
• New satellites will measure
fluorescence.
• Still working on REIP.
What Can These Two Papers Tell
Us about Stress in Trees Today?
Today scientists know about 80 “indices” or
messages in light waves which they can interpret
to understand tree health. We are trying to learn
more of the language of light, to become as
“photonic” as we are “literate.”
Copyright 2011 University of New Hampshire.