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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) C.R. Howell October 2008 2 What is a Phytotron? • Controlled Environment Facility • Growth chambers can control many factors: – – – – – – – Soil type Air Temperature Light levels (total & UV) Carbon dioxide concentration Relative humidity Nutrients Air pollutants C.R. Howell October 2008 3 Evidence for Influence of Human Activities on Atmospheric CO2 Levels “Industrial Revolution” C.R. Howell October 2008 4 Long timeline Atmospheric CO2 Levels C.R. Howell October 2008 5 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) C.R. Howell October 2008 6 Ice Core Measurements at Vostok C.R. Howell October 2008 7 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). C.R. Howell October 2008 8 Recent Atmospheric CO2 Concentration Data C.R. Howell October 2008 9 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) C.R. Howell October 2008 10 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) C.R. Howell October 2008 11 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 C.R. Howell October 2008 12 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” C.R. Howell October 2008 13 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 C.R. Howell October 2008 14 FACE Sites C.R. Howell October 2008 15 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 C.R. Howell October 2008 16 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 17 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 18 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 C.R. Howell October 2008 19 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 C.R. Howell October 2008 + p 15O + d Target: water 16O 20 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 C.R. Howell October 2008 21 Single Detector Measurements C.R. Howell October 2008 22 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 C.R. Howell October 2008 23 Total Sink 2D Imaging C.R. Howell October 2008 24 y (cm) For Example C.R. Howell x (cm) October 2008 25 y (cm) For Example C.R. Howell x (cm) October 2008 26 Immediate Plans • Develop system for continuous loading measurements • Develop system for nutrient uptake studies • Continue root exudate experiments • Develop high-resolution 2D PET imager C.R. Howell October 2008 27 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 C.R. Howell October 2008 28