Research is currently under way at Heriot-Watt University (Edinburgh, UK) to develop a robust, portable, non-invasive system for field measurements of xylem and phloem sap flow in trees. The system uses a near-infrared laser source (l = 812 nm) for local application of heat pulses to the stem. The dimensions of the heated area are typically 1 mm high × 5 mm wide; the optical power at the sample is ca. 500 mW and causes a localised temperature rise of 5–10 °C. An infrared camera monitors the temporal evolution of the temperature field around the point of heating; thermometric profiles are used for the calculation of flow velocities. Detection of xylem and phloem by our technique has been demonstrated (Helfter et al.). The performance of the laser-based approach was compared with xylem velocities determined by MRI flow imaging (Windt, etl al.) at the Wageningen NMR Centre (NL). The custom-built MRI system consists of a 0.72 T electromagnet of planar geometry allowing for lateral insertion of the plant and simultaneous MRI and heat pulse measurements. A near 1:1 agreement between MRI and heat pulse xylem flow velocities was found in both Golden Alder and Silver Birch saplings over several night and day cycles.
|Journal||Comparative Biochemistry and Physiology - Part A: Molecular & Integrative Physiology|
|Issue number||4, Supplement|
|Publication status||Published - Apr 2007|