Methods and instruments used to analyse sap flow in plants. A. Schematic representation of different methods used to measure sap flow
velocity. In heat-based methods, heat sensors (heat pulse velocity, heat field deformation, or thermal dissipation) are installed radially into a segment. In
radioisotope or dye methods, tracers are injected into the xylem or uptaken from a cut segment. B. Methods used to measure negative pressure in the
xylem. The observation scale and measurement target (i.e. cell, tissue, or organ) differ between indirect (i.e. pressure bomb, centrifugation) or direct (i.e.
cell pressure probe) methods. C. Simultaneous visualization of xylem structure and sap flow using magnetic resonance, neutron or synchrotron X-ray
imaging methods. The temporal and spatial resolutions vary for each imaging method.