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INTERNATIONAL

Plant and Soil Water Potential. INTERNATIONAL. Research Background. Hawkesbury Forest Experiment University of Western Sydney, Richmond, NSW Whole Tree Chambers CO 2 x Drought Experiment. Research Background. Ambient CO 2 : 380ppm Elevated CO 2 : Am + 300ppm

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INTERNATIONAL

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  1. Plant and Soil Water Potential INTERNATIONAL

  2. Research Background • Hawkesbury Forest Experiment • University of Western Sydney, • Richmond, NSW • Whole Tree Chambers • CO2 x Drought Experiment

  3. Research Background • Ambient CO2: 380ppm • Elevated CO2: Am + 300ppm • Irrigated: 10mm every 3 days • Drought: no water • Control treatment • My Job: The Drought

  4. Quantifying Drought • Rainfall • Soil Water Content • Volumetric • Gravimetric • Soil Water Availability • Dependent on Soil Texture • Soil Water Potential Image: Craig Barton

  5. Definition • Water Potential: • Free energy associated with water • Free energy is the potential to do work • Water moves from higher to lower potentials • Water moves from mountains to ocean

  6. Definition • Water Potential Units of Measurement: High Potential Low Potential Source: Decagon Inc.

  7. Soil-Plant-AtmosphereContinuum Low Potential Atmosphere = -100 Bar Leaf air = -7.0 Bar Leaf cell = -1.0 Bar Trunk = -0.8 Bar Soil = -0.33 Bar High Potential

  8. Quantifying Drought - Atmosphere • Weather Station: • Vapour Pressure Deficit • Armidale in Summer approx. 3 kPa • Sydney in Summer approx. 6 kPa • Alice Springs in Summer approx. 10 kPa • Potential Evaportranspiration • Penman-Montieth Equation

  9. Quantifying Drought - Soils Source: Decagon Inc.

  10. Quantifying Drought - Soils • Thermocouple inside ceramic • Heat pulse sent through sensor • Temperature rise measured • Dry soil = large increase • Wet soil = small increase

  11. Quantifying Drought - Soils • Thermal Matric Potential Sensor: • Advantages: • Highly accurate • Large measurement range • Logging capability • Disadvantages: • Calibration required • Careful installation

  12. Quantifying Drought - Soils • Moisture Release Curves: • Quantifying soil moisture content Against soil water potential for Varying Soil Textures • Standard practice to measure Between Field Capacity and Plant Wilting Point: -0.33 to -15 Bar Graph Source: Remko Duursma, UWS

  13. Graph Source: Remko Duursma, UWS

  14. Moisture Release Curves: • Advantages: • Relatively cheap • Established methodology • Disadvantages: • Time consuming (months) • Soils highly variable • Many curves needed • Reliance on extrapolation Image: Craig Barton

  15. Quantifying Drought - Soils • Moisture Release Curves: • Advantages: • Cheap (per sample) • Fast response time (one day) • Many curves can be constructed • Larger portion of curve (-1000MPa) • Disadvantages: • Poor resolution at wet end of curve • (Pressure plate can resolve wet end)

  16. Soil-Plant-AtmosphereContinuum Low Potential Atmosphere = -100 Bar Leaf air = -7.0 Bar ? Leaf cell = -1.0 Bar Trunk = -0.8 Bar Soil = -0.33 Bar High Potential

  17. Quantifying Drought - Plants • Leaf Water Potential with WP4-T: • Advantages: • True leaf water potential • Disadvantages: • Tricky methodology • Slow response time (30 minutes) • Rarely done

  18. Quantifying Drought - Plants • Leaf Water Potential with Pressure Bomb:

  19. Quantifying Drought - Plants • Leaf Water Potential with Pressure Bomb: • Advantages: • Proven, accurate technique • Widely used, easy to do • Data is potentially powerful • Disadvantages: • Spot measurement, destructive • Slow sampling (for large sample size) • Xylem water potential

  20. Predawn Leaf Water Potential Ambient CO2 Results Only: Graph Source: David Ellsworth, UWS

  21. Midday Leaf Water Potential Graph Source: David Ellsworth, UWS

  22. Unexpected Results Ambient Drought Elevated Drought Graph Source: Remko Duursma, UWS

  23. Combining Instruments Leaf Water Potential + Neutron Probe Soil Moisture Graph Source: Remko Duursma, UWS

  24. Combining Instruments Leaf Water Potential + Neutron Probe Soil Moisture +Soil Water Potential= COMPLETE STORY Elevated Drought Ambient Drought Graph Source: Remko Duursma, UWS

  25. Diurnal Leaf Water Potential What regulates Plant Water Status? Stomatal Closure? Hydraulic Architecture? Graph Source: Michael Forster, UWS; Derek Eamus, UTS

  26. Combining Instruments Leaf Water Potential + Sap Flow (Tree Water Use) Graph Source: Michael Forster, UWS; Derek Eamus, UTS

  27. Combining Instruments Graph Source: Michael Forster, UWS; Derek Eamus, UTS Slope of lines is similar No difference in soil to leaf hydraulic pathway Plant water status under control of stomata

  28. Combining Instruments Leaf Water Potential + Stomatal Conductance (Porometer) Graph Source: David Ellsworth, UWS;

  29. Pressure Bomb Data

  30. Stem Psychrometer Data Graph Source: Alec Downey, ICT International

  31. PSY-1 New Instrument

  32. Psychrometer/Hygrometer

  33. Psychrometer/Hygrometer

  34. Definition • Water Potential Units of Measurement: High Potential Low Potential

  35. A New Generation

  36. A New Generation - Psychrometer

  37. The Ideal System Atmosphere Weather Station Leaves WP4-C Porometer Pressure Bomb Psychrometer Sap Flow Stem / Trunk Roots Thermal Matric Potential Sensor WP4-C Soil Moisture Sensors Soil

  38. Continuous Logging Options Atmosphere Weather Station Leaves Psychrometer Sap Flow Stem / Trunk Roots Thermal Matric Potential Sensor Soil Moisture Sensors Soil

  39. Acknowledgements Thank you to David Ellsworth, David Tissue, Craig Barton, Derek Eamus and Remko Duursma for kind permission to use data. The Hawkesbury Forest Experiment involved researchers from: University of Western Sydney, University of Technology, Sydney, University of New South Wales, Macquarie University, Industry & Investment, NSW, and Swedish University of Agricultural Sciences All researchers involved with the HFE acknowledge the provision of funding by the Australian Government's Department of Climate Change and the Department of Agriculture, Fisheries and Forestry for the Hawkesbury Forest Experiment.

  40. ICT International Pty Ltd Solutions for soil, plant and environmental research www.ictinternational.com.au sales@international.com.au Phone: 61 2 6772 6770 Fax: 61 2 6772 7616 PO Box 503, Armidale, NSW, Australia, 2350 International

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