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Enabling better global research outcomes in soil, plant & environmental monitoring.

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.

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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
  • 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.
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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).
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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.
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Results:
  • Basic interpretation of data on visual inspection:
  • Diurnal and nocturnal sap flow
  • Warm and Cool Weather

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Analysis from Sap Flow Tool software: (www.sapflowtool.com)  Indicated the rose plant used on average 0.12 Litres of water per day.
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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.
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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.
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Results

Statistical Analysis
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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