C.R. Howell October 2008 1 Measuring Dynamical Measuring Dynamical Responses of Plants to Responses of Plants to Environment Change Using Environment Change Using Short-lived Radioisotope Short-lived Radioisotope Calvin Howell Duke University Physics Triangle Universities Nuclear Laboratory
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C.R. HowellOctober 20081 Measuring Dynamical Responses of Plants to Environment Change Using Short-lived Radioisotope Calvin Howell Duke University Physics.
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C.R. Howell October 2008 1
Measuring Dynamical Responses of Measuring Dynamical Responses of Plants to Environment Change Using Plants to Environment Change Using
Evidence for Influence of Human Activities on Evidence for Influence of Human Activities on Atmospheric CO2 LevelsAtmospheric CO2 Levels
“Industrial Revolution”
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Long timeline Atmospheric CO2 Levels
Calvin Howell
Data taken from ice cores more that 3 km deep.1000 m = 64.7 kyrs2000 m = 136.8 kyrs
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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"EAltitude: 11484 ft3 (500 m) above sea levelAverage Annual Temperature: -67°F (-55°C)
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Ice Core Measurements at Vostok
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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).
will double by the end will double by the end of this century!of this century!
How will plants respond?How will plants respond?
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FACE StudiesFACE 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– Initially, trees grow faster in COInitially, trees grow faster in CO2 2
enhanced environment, but then enhanced environment, but then grow a slower rate than trees grow a slower rate than trees grown in at ambient COgrown in at ambient CO22 level level
Duke FACTS-I Aerial ViewDuke FACTS-I Aerial View
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FACE SitesFACE Sites
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Introduction to Plant Studies with Introduction to Plant Studies with RadioisotopesRadioisotopes
• 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
1. Studies of CO2 uptake and carbon translation under different environmental conditions
2. Root exudate measurements 3. Nutrient uptake and translocation under different environmental
conditions
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Plant Physiology 101Plant Physiology 101a) Sugars loaded into a sieve tubeb) Loading of the phloem sets up
water potential gradient that facilitates movement of water into dense phloem sap from the neighboring xylem
c) As hydrostatic pressure in phloem sieve tube increases, pressure flow begins, and sap moves through the phloem
d) At the sink, incoming sugars actively transported out of phloem and removed as complex carbohydrates
e) Loss of solute produces high water potential in phloem, and water passes out, returning eventually to xylem http://home.earthlink.net/~dayvdanls/plant_transport.html
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Carbon-11 ProductionCarbon-11 Production
p + 14N 11C + ++1
5
2 3 4
2
3
1 Produce H- ions in negative ion source
4
5
Accelerate H- ions toward +5MV terminal
Strip off electrons with carbon foil (H- p)
Accelerate protons away from +5MV terminal
Bend p in magnet and collide on 14N target
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Radioisotope Production
1. 11CO2 (half life = 20 min.)
14N + p 11C + Target: gas
3. 18F- (half life = 109 min.) 18O + p 18F + n
Target: 18O enriched water
2. 13NO3- (half live = 10 min.)
16O + p 13N + Target: 18O depleted water
4. H218O (half life = 2 min.)
16O + p 15O + d
Target: water
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Single Detector MeasurementsSingle 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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Single Detector MeasurementsSingle Detector Measurements
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Statistical Model
Extract Physically Significant Quantities:
(1)(1) GainGain – fraction of inputinput that shows up at the outputoutput(2)(2) Average transit timeAverage transit time
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)