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Transpiration Explorer

Explore how plants lose water through transpiration. Adjust stomatal aperture, environmental conditions, and plant characteristics to see how transpiration rates change. Visualize the cohesion-tension mechanism of water transport and measure water uptake with a virtual potometer.

Plant Cross-Section

Controls

Stomatal Aperture8.0 μm
012 μm
Stomatal Density200 /mm²
50500 /mm²
Leaf Area50 cm²
5200 cm²
Humidity50 %
5100 %
Wind Speed1.5 m/s
010 m/s
Temperature25.0 °C
545 °C
Light Intensity1000 μmol/m²/s
02000 μmol/m²/s

Results

Transpiration: 3.073 mmol H₂O/m²/s

Active transpiration

Calculated Values

Stomatal Conductance0.9930 mol/m²/s
VPD1.584 kPa
Transpiration Rate3.073 mmol/m²/s

Current Conditions

Aperture8.0 μmDensity200 /mm²Leaf Area50 cm²Temperature25.0°CHumidity50%Sat. Vapor Pressure3.169 kPa

Transpiration Equation

E=gs⋅VPDPatmE = g_s \cdot \frac{\mathrm{VPD}}{P_{\mathrm{atm}}}

Stomatal Aperture Response

Transpiration rate vs stomatal aperture width at current conditions

Transpiration Rate

Temperature Response

Transpiration rate vs temperature at RH = 50%

Humidity Response

Transpiration rate vs relative humidity at T = 25.0°C

Reference Guide

Transpiration Rate

Transpiration rate depends on stomatal conductance and the vapor pressure deficit between the leaf interior and the surrounding air.

E=gs⋅VPDPatmE = g_s \cdot \frac{\mathrm{VPD}}{P_{\mathrm{atm}}}

Where E is transpiration rate (mol/m²/s), g_s is stomatal conductance, VPD is the vapor pressure deficit, and P_atm is atmospheric pressure.

Vapor Pressure Deficit

VPD is the difference between the amount of moisture the air can hold (saturation) and the actual moisture present. Higher VPD drives faster transpiration.

VPD=es(T)×(1−RH100)\mathrm{VPD} = e_s(T) \times \left(1 - \frac{\mathrm{RH}}{100}\right)

Hot, dry conditions create high VPD, pulling water out of leaves faster. Humid conditions reduce VPD, slowing transpiration.

Magnus Formula

The Magnus formula calculates saturation vapor pressure as a function of temperature. It is the key to understanding why warm air drives more transpiration.

es=0.611×exp⁡ ⁣(17.27 TT+237.3)e_s = 0.611 \times \exp\!\left(\frac{17.27\,T}{T + 237.3}\right)

Where e_s is in kPa and T is temperature in degrees Celsius. The exponential nature means small temperature increases lead to large VPD changes.

Cohesion-Tension Theory

Water moves from roots to leaves through xylem vessels under negative pressure (tension). Transpiration creates this tension at the top, pulling water upward through cohesive hydrogen bonds.

Ψleaf=Ψsoil−ρgh−Rfriction\Psi_{\text{leaf}} = \Psi_{\text{soil}} - \rho g h - R_{\text{friction}}

The water potential at the leaf (in MPa) decreases with height due to gravity and frictional resistance in the xylem. Tall trees can develop tensions exceeding -2 MPa.