A validation, comparison and error analysis of two heat-pulse methods for measuring sap flow in Eucalyptus marginata...

Area of Science:

• Plant Physiology
• Forest Ecology
• Environmental Science

Background:

• Accurate measurement of sap flow is crucial for understanding plant water use and transpiration.
• Established methods like the compensation heat-pulse method (CHPM) have limitations in measuring low flow rates.

Purpose of the Study:

• To validate and compare the compensation heat-pulse method (CHPM) and the heat-ratio method (HRM) for measuring sap flow in Eucalyptus marginata (jarrah).
• To assess the accuracy and limitations of both methods under various flow conditions.

Main Methods:

• Sap flow was measured in potted jarrah saplings using CHPM and HRM.
• Measurements were compared against a weighing lysimeter under well-watered conditions.
• Sensor alignment, sapwood area estimation, and total sap flow calculation methods were analyzed for potential errors.

Main Results:

• Both CHPM and HRM showed similar sap flow rates during daylight hours (0.1-0.5 kg h⁻¹), with no significant difference compared to lysimeter measurements (P<0.001).
• HRM accurately measured low nocturnal sap flow (< 0.1 kg h⁻¹), whereas CHPM failed below a threshold velocity.
• HRM demonstrated superior error correction for sensor spacing and measurement fluctuations compared to CHPM.

Conclusions:

• Both CHPM and HRM are valid for measuring transpiration in jarrah and other woody species, each with specific constraints.
• The heat-ratio method (HRM) is more favorable for accurately measuring low sap flow rates and offers better resistance to measurement errors.
• Potential errors in daily sap flow calculations stem from sensor misalignment, sapwood area estimation, and data acquisition methods.