Chapter 6. Methods for assessment of hydraulic conductance and embolism extent in grapevine organs

The aim of this chapter is to assess the interplay of hydraulic conductance and xylem embolism (cavitation) in root, in shoot, in leaf and in the whole grapevine. To measure hydraulic conductance, three main methods are available, which are based on evaporating (EFM), pulling (VPM) or pushing (HPM) water out of the plant organ. The three methods are expected to give similar results upon plant water status. Under drought, hydraulic conductance assessment must take into account the extent of embolism. EFM does not modify xylem cavitation and gives good estimates of hydraulic conductance, even if it does not give direct evi-dence of the embolism phenomenon. VPM involves pulling water through the or-gan using a vacuum pump, but it is limited by the atmospheric pressure (about 0.1 MPa); when the pulling-tension does not exceed the organ water potential, pres-ence of embolism is not perturbed. The HPM is the easiest method to modulate a wide range of pressures, forcing flows into the sample; HPM measurements can displace native embolism. Extent of embolisms is represented as Percent Loss of Conductivity (PLC) of organ-segments. By imposing an appropriate pressure to HPM systems, it is possible to assess organ-segment PLC.