Measuring Dynamical Responses of Plants to Environment Change Using Short-lived Radioisotope

C.R. Howell October 2008 1

Measuring Dynamical Responses of Measuring Dynamical Responses of Plants to Environment Change Using Plants to Environment Change Using

Short-lived RadioisotopeShort-lived Radioisotope

Calvin Howell

Duke University Physics

Triangle Universities Nuclear Laboratory


C.R. Howell (Physics)C. Reid (Biology)E. Bernhardt (Biology)A.S. Crowell (Physics Postdoc)M. Kiser (Physics graduate student)R. Phillips (Biology Postdoc)

Measuring Dynamic BiologicalResponses in Plants using Radioisotopes

Collaboration


What is a Phytotron?What is a Phytotron?

• CControlled EEnvironment FFacility• Growth chambers can control many factors:

– Soil type

– Air Temperature

– Light levels (total & UV)

– Carbon dioxide concentrationCarbon dioxide concentration

– Relative humidity

– Nutrients

– Air pollutants


Evidence for Influence of Human Activities on Evidence for Influence of Human Activities on Atmospheric CO2 LevelsAtmospheric CO2 Levels

“Industrial Revolution”


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


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)


Ice Core Measurements at Vostok


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).

http://www.esrl.noaa.gov/

http://www.cmdl.noaa.gov/

http://www.noaa.gov/


Recent Atmospheric CO2 Concentration Data

Calvin Howell

NOAA - National Oceanic and Atmosphere AdministrationPaleoclimatology


Carbon BudgetCarbon Budget

Sinks in units of billions of metric tons of carbon (GtC)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)Fluxes in units of billions of metric tons of carbon per year (GtC/year)

Intergovernmental Panel on Climate Change (IPCC): Climate Change 2001, “The Carbon Cycle and Atmospheric Carbon Dioxide”


Carbon BudgetCarbon Budget

Sinks in units of billions of metric tons of carbon (GtC)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)Fluxes in units of billions of metric tons of carbon per year (GtC/year)



Interesting AsideInteresting Aside

• 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

13 mpg

36 mpg

22 mpg

18 mpg

65 mpg

http://www.sierraclub.org/globalwarming/suvreport/pollution.asp

Top 5 CO2 Emitters:1. U.S.2. China3. Russia 4. Japan5. U.S. autos

http://www.sierraclub.org/globalwarming/suvreport/pollution.asp


MotivationsMotivations


Climate models predict Climate models predict atmospheric COatmospheric CO22 levels levels

will double by the end will double by the end of this century!of this century!

How will plants respond?How will plants respond?


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


FACE SitesFACE Sites


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

– Present studies at: Julich, Germany; Univ. Tokyo; BNL; TUNL-Duke


Planned Research at the TUNL-Phytotron Facility

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


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


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


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


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


Single Detector MeasurementsSingle Detector Measurements


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)

Yk = - a1 Yk-1 - a2 Yk-2 - … - an Yk-n + b0 Uk + b1 Uk-1 + … + bm Uk-m

Leaf

Shoot

Root

Source

TotalSink

Sink A

Sink B

respiration

respiration

respiration, exudation


2D Imaging2D Imaging


For ExampleFor Example

x (cm)

y (c

m)


For ExampleFor Example

x (cm)

y (c

m)


Immediate PlansImmediate Plans

• Develop system for continuous loading measurements

• Develop system for nutrient uptake studies

• Continue root exudate experiments

• Develop high-resolution 2D PET imager


High resolution 2D imagers

5 cm x 5 cm x 1.5 cm2mm x 2mm pixels (0.1 mm gap)

20 cm x 30 cm field of view

Documents

Measuring Dynamical Responses of Plants to Environment Change Using Short-lived Radioisotope