Xylem hydraulic conductivity related to conduit dimensions along chrysanthemum stems

The stem xylem conduit dimensions and hydraulic conductivity of chrysanthemum plants (Dendranthema x grandiflorum Tzvelev cv. Cassa) were analysed and quantified. Simple exponential relations describe conduit length distribution, height dependency of conduit length distribution, and height dependency of stem hydraulic conductivity. These mathematical descriptions can be used to model the xylem water transport system. Within a chrysanthemum stem of 1.0 m, the conduit half-length (the length within which 50% of the conduits have their end) was 0.029 m at soil surface and decreased by half at a height of 0.6 m. With each 0.34 m increase in height up the stem, the hydraulic conductivity decreased by 50%. The resistance calculated from conduit lumen characteristics was 70% of the measured resistance. The remaining unexplained part of the hydraulic resistance is at least partly caused by inter-conduit connections.