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Limits to Tree Height

Explore the impacts of pressure differentials on plant development, from soil to atmosphere. Learn about the challenges plants face, like stem cavitation and embolism, affecting their maximum height potential.

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Limits to Tree Height

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  1. Limits to Tree Height 2 November 2005 PLB 203

  2. The Soil-Plant-Atmosphere Continuum Cohesion Adhesion

  3. Lowest Pressure -1.2 MPa -1.0 MPa -0.1 MPa Highest Pressure Pressure of the Atmosphere: 135 MPa * ln (RH/100) At 99% humidity pull of the atmosphere is -1.36 MPa At 30% humidity = -162 MPa Water flows from high pressure to low pressure Pa = N/m2 MPa = 106 Pa

  4. Pressure Differences High Blood Pressure in Humans: 140 mm Hg High Pressure in Plants: -12 MPa = -91,200 mm Hg OVER 600 TIMES THE PRESSURE EXPERIENCED BY HUMANS!!

  5. Stem cavitation

  6. What happens here? Reduced stomatal conductance Reduced transpiration Reduced photosynthesis 100 % 50 % % Embolism 0 % High (0 MPa) Low (-5 MPa) Pressure

  7. Ψ50 = Pressure Potential at 50 % Embolism 100 % 50 % % Embolism or % loss in conductivity 0 % High (0 MPa) Low (-5 MPa) Pressure

  8. Sperry et al. 1995

  9. Ψ50 = -2 MPa Ψx = Ψs + Ψg + Ji* ri Humid soil = 0 MPa Pressure due to gravitiy = -0.0098 MPa m-1. Transpirational pressure times path resistivity ≈ 1/3 of total pressure -2 MPa = 0 MPa + -0.0098x + -2 MPa * (1/3) Maximum height = 136 m

  10. Earth Mars Calculate the maximum height that these plants could obtain before reaching Ψ’s more negative than their Ψ50. Ψx = Ψs + Ψg + Ji* ri Humid soil = 0 MPa Hydrostatic gradient of water is -0.0098 MPa m-1. Transpirational pressure times path resistivity = 1/3 of total pressure Why aren’t these plants this tall? Some Ψ50’s for plants: 153 m 61 m Poplar = -0.9 MPa 6.8 m Button bush = -0.1 MPa 17 m 2381 m Juniper = -14 MPa 952 m What heights could these plants theoretically reach on Mars where the pressure gradient of water is 0.4 times that on Earth?

  11. Cohesion Adhesion Path Resistivity Pressure of stomatal closure Direction of Water Flow

  12. Cells with healthy turgor Cells with unhealthy turgor

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