HRM Sap Flow and Small Stems
Sap Flow in Small Stems outlines how the SFM1 Sap Flow Meter can be installed on stems with a diameter of at least 1cm for precise measurements.
The SFM1 Sap Flow Meter uses the Heat Ratio Method (HRM)
- Measures sap flow (water movement) or transpiration in woody plants
- Data can be used to accurately measure total plant water use on a hourly or daily basis
- SFM1 Sap Flow Meter can measure stems as narrow as 1cm
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Self contained, stand alone system
- IP65 rated water proof enclosure
- Low power demand
- Extensive cables and battery systems not needed
- 16GB memory capacity
- USB, SD Card or wireless data transfer
The sensors measure heat pulse velocity by obtaining the ratio of downstream sapwood temperature to upstream sapwood temperature following the release of a heat pulse.
HRM Accuracy
Aim: To measure sap flow in a rose bush with a narrow diameter stem and to correlate measured data with environmental variables (vapour pressure deficit and solar radiation).
Methods: Species: Rose, cultivar Grimaldi approximately 0.6m tall, stem diameter 1.4cm
Sap Flow measured using Heat Ratio Method (Burgess et al . 2001*).
Linear regression of Sap Flow versus VPD and Solar Radiation used to assess accuracy of data.
Cover needles with foam insulation in order to avoid external heat influences.
Results:
- Basic interpretation of data on visual inspection:
- Diurnal and nocturnal sap flow
- Warm and Cool Weather
Analysis from Sap Flow Tool software: (www.sapflowtool.com) Indicated the rose plant used on average 0.12 Litres of water per day.
Results
Environmental Drivers of Sap Flow: Vapour Pressure Deficit (VPD).
Below is an example of sap flow data from HRM sensor inserted in a narrow rose stem over a seven day period.
Results
Environmental Drivers of Sap Flow: Solar Radiation.
Below is an example of sap flow data from HRM sensor inserted in a narrow rose stem over a seven day period.
Results
Statistical Analysis
Note: Data are sum of diurnal sap flow, VPD and solar radiation; data were square – root transformed to meet assumptions of normality; p – value less than 0.05 indicate data are significantly correlated; larger R 2 value in Sap Flow vs VPD indicates VPD is a stronger driver of sap flow than solar radiation in this rose plant at this location during this weather period.
Summary
- With careful experimental design and installation, sap flow of stems with a diameter of at least 1cm can be accurately measured
- Needles must be insulated to buffer external heat influences such as direct sunlight
- Sap flow data show a significant relationship with environmental drivers Vapour Pressure Deficit and Solar Radiation
- The rose plant in this example was found to use on average 0.12 Litres of water per day under temperate summer weather conditions
