Transcript Verification of Selected Neutron

Measuring Dynamical Responses of
Plants to Environment Change Using
Short-lived Radioisotope
Calvin Howell
Duke University Physics
Triangle Universities Nuclear Laboratory
C.R. Howell
October 2008
1
Measuring Dynamic Biological
Responses in Plants using Radioisotopes
Collaboration
C.R. Howell (Physics)
C. Reid (Biology)
E. Bernhardt (Biology)
A.S. Crowell (Physics Postdoc)
M. Kiser (Physics graduate student)
R. Phillips (Biology Postdoc)
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October 2008
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What is a Phytotron?
• Controlled Environment Facility
• Growth chambers can control many factors:
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Soil type
Air Temperature
Light levels (total & UV)
Carbon dioxide concentration
Relative humidity
Nutrients
Air pollutants
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October 2008
3
Evidence for Influence of Human Activities on
Atmospheric CO2 Levels
“Industrial Revolution”
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October 2008
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Long timeline Atmospheric CO2 Levels
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October 2008
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The Vostok Station in Antarctica
Information:
The coldest recorded temperature on Earth, -128.6°F (-89.2°C) was measured here on
July 21, 1983.
Latitude/Longitude: 78°27'51"S 106°51'57"E
Altitude: 11484 ft3 (500 m) above sea level
Average Annual Temperature: -67°F (-55°C)
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October 2008
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Ice Core Measurements at Vostok
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October 2008
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Atmospheric CO2 Concentration Measurements
Since the 1950’s
•
Mauna Loa Observatory (MLO) is an atmospheric baseline station. Since the mid 1950's
MLO has been continuously monitoring and collecting data relating to atmospheric
change . The observatory is under the Earth System Research Laboratory (ESRL) Global Monitoring Division (GMD) which is part of the National Oceanic and
Atmospheric Administration (NOAA).
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October 2008
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Recent Atmospheric CO2 Concentration Data
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October 2008
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Carbon Budget
Intergovernmental Panel on Climate Change (IPCC): Climate Change 2001,
“The Carbon Cycle and Atmospheric Carbon Dioxide”
Sinks in units of billions of metric tons of carbon (GtC)
Fluxes in units of billions of metric tons of carbon per year (GtC/year)
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October 2008
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Carbon Budget
Intergovernmental Panel on Climate Change (IPCC): Climate Change 2001,
“The Carbon Cycle and Atmospheric Carbon Dioxide”
Sinks in units of billions of metric tons of carbon (GtC)
Fluxes in units of billions of metric tons of carbon per year (GtC/year)
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October 2008
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Interesting Aside
Top 5 CO2 Emitters:
1. U.S.
2. China
3. Russia
4. Japan
5. U.S. autos
13 mpg
• Total tonnage of CO2
produced by vehicles over
124,000 mile lifetime
• Assuming ~10 year lifetime,
vehicles emit more than
their own weight in CO2 per
year
18 mpg
22 mpg
36 mpg
65 mpg
http://www.sierraclub.org/globalwarming/suvreport/pollution.asp
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October 2008
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Motivations
Climate models predict
atmospheric CO2 levels
will double by the end
of this century!
How will plants respond?
Intergovernmental Panel on Climate Change (IPCC): Climate Change 2001,
“The Carbon Cycle and Atmospheric Carbon Dioxide”
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October 2008
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FACE Studies
• Free Air CO2 Enrichment
(FACE) experiments
– Large-scale research programs to
study effects of increased CO2
levels
– Many environmental variables
– Difficult to correlate growth
parameters with high precision
• Findings from forest stands
Duke FACTS-I Aerial View
– Initially, trees grow faster in CO2
enhanced environment, but then
grow a slower rate than trees
grown in at ambient CO2 level
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October 2008
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FACE Sites
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October 2008
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Introduction to Plant Studies with
Radioisotopes
•
14C
used in mid-1940’s
– Long half-life (~5730 years)
– Weak beta emitter
– Tracer measured by destructive harvesting
• Use of 11C for in vivo studies demonstrated in 1963
• 1973 – More and Troughton at the Department of
Scientific and Industrial Research in New Zealand showed
that useful amounts of 11C can be produced using small
van de Graaf accelerators
– Labs in USA, Canada, Scotland, New Zealand, and Germany
start using 11C for mechanistic studies of photosynthate
transport in the mid 1970’s
– Present studies at: Julich, Germany; Univ. Tokyo; BNL;
TUNL-Duke
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October 2008
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Planned Research at the
TUNL-Phytotron Facility
1.
2.
3.
C.R. Howell
Studies of CO2 uptake and carbon translation under different
environmental conditions
Root exudate measurements
Nutrient uptake and translocation under different environmental
conditions
October 2008
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Plant Physiology 101
a)
b)
c)
d)
e)
Sugars loaded into a sieve tube
Loading of the phloem sets up
water potential gradient that
facilitates movement of water into
dense phloem sap from the
neighboring xylem
As hydrostatic pressure in
phloem sieve tube increases,
pressure flow begins, and sap
moves through the phloem
At the sink, incoming sugars
actively transported out of phloem
and removed as complex
carbohydrates
Loss of solute produces high
water potential in phloem, and
water passes out, returning
eventually to xylem
C.R. Howell
http://home.earthlink.net/~dayvdanls/plant_transport.html
October 2008
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Carbon-11 Production
p + 14N  11C + a
+
1
2
3
4
5
1
Produce H- ions in negative ion source
2 Accelerate H- ions toward +5MV terminal
3 Strip off electrons with carbon foil (H-  p)
4
Accelerate protons away from +5MV terminal
5
Bend p in magnet and collide on 14N target
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October 2008
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Radioisotope Production
1. 11CO2 (half life = 20 min.)
3. 18F- (half life = 109 min.)
+ p  11C + a
Target: gas
+ p  18F + n
Target: 18O enriched water
14N
2.
13NO 3
18O
(half live = 10 min.)
4. H218O (half life = 2 min.)
+ p  13N + a
Target: 18O depleted water
16O
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October 2008
+ p  15O + d
Target: water
16O
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Single Detector Measurements
• Use detectors
collimated for
specific areas of
plant to trace carbon
allocation on a
coarse (source/sink)
scale
• Develop quantitative
flow models to
describe dynamics
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October 2008
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Single Detector Measurements
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October 2008
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Statistical Model
respiration
Leaf
Source
Shoot
Sink A
Root
Sink B
respiration
respiration, exudation
Discrete observation times: tk where k = 0, 1, 2, …
Yk = counts in Sink B at time tk (output)
Uk = counts in Total Sink at time tk (input)
Yk = - a1 Yk-1 - a2 Yk-2 - … - an Yk-n + b0 Uk + b1 Uk-1 + … + bm Uk-m
Extract Physically Significant Quantities:
(1) Gain – fraction of input that shows up at the output
(2) Average transit time
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October 2008
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Total
Sink
2D Imaging
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October 2008
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y (cm)
For Example
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x (cm)
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y (cm)
For Example
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x (cm)
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Immediate Plans
• Develop system for continuous loading
measurements
• Develop system for nutrient uptake studies
• Continue root exudate experiments
• Develop high-resolution 2D PET imager
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High resolution 2D imagers
5 cm x 5 cm x 1.5 cm
2mm x 2mm pixels (0.1 mm gap)
20 cm x 30 cm field of view
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