[Application of three heat pulse technique-based methods to determine the stem sap flow]

Area of Science:

• Forest Ecology
• Plant Physiology
• Hydrology

Background:

• Understanding tree water use is vital for forest ecology and ecosystem water exchange.
• Sap flow methodology provides critical data on tree transpiration.
• Tri-probe heat pulse sensors are commonly used for thermal measurements.

Purpose of the Study:

• To compare the accuracy and reliability of different sap flow density (Vs) measurement methods using tri-probe heat pulse sensors.
• To evaluate the performance of Heat-Ratio Method (HRM), T-Max method, and Single-Probe Heat Pulse Probe (SHPP) against a standard Thermal Diffusion Probe (TDP).
• To determine the optimal method or combination of methods for measuring stem sap flow in Salix matsudana.

Main Methods:

• Utilized tri-probe heat pulse sensors to measure Salix matsudana sap flow density (Vs).
• Applied Heat-Ratio Method (HRM), T-Max method, and Single-Probe Heat Pulse Probe (SHPP) for Vs estimation.
• Compared results with measurements from Grainer's Thermal Diffusion Probes (TDP).

Main Results:

• A stable measurement stage was reached approximately five weeks after sensor installation.
• Early-stage Vs measurements were 135%-220% higher than stable-stage measurements.
• HRM, T-Max, and SHPP showed strong linear correlations with TDP (R²=0.93, 0.73, 0.91 respectively).
• SHPP and HRM achieved the highest correlation (R²=0.94) and HRM excelled in measuring low and reverse sap flow.
• SHPP offered simplicity and accuracy but couldn't determine flow direction; T-Max had higher errors and limitations at low flow rates.

Conclusions:

• SHPP and HRM are highly promising for accurate sap flow density (Vs) measurements.
• The T-Max method has limitations and is best used in conjunction with other methods.
• Choosing the appropriate sap flow measurement technique or combination depends on specific research objectives.