Fig. 13.
Modelling of root hydraulic conductance (L, m3 s−1 MPa−1) of barley plants grown under nutrient-sufficient control conditions or on media low in N or P (low-N, low-P). Hydraulic conductance was calculated from data on cortex cell hydraulic conductivity (Lp, m3 m−2 s−1 MPa−1) using cell dimensions and the difference in water potential between cortex cells and root medium; or using data on exudation Lp, together with data on root surface area; or using data on plant transpirational water loss together with data on root surface area and the water potential difference between xylem and root medium, being the driving force (DF) of radial root water uptake. A measured value of DF between cortex cells and root medium and a value of DF derived from the determination of shoot water potential as part of a previous study (Suku et al., 2014) was used. Values of cell Lp were available for control and low-N plants for all root positions and types analysed; a gross approximation needed to be made for lateral roots of low-P plants, which were not analysed for Lp, by using the mean value of control and low-N plants. All abbreviations are explained in the legend contained within the figure.