Gas diffusion kinetics drive embolism spread in angiosperm xylem: evidence from flow-centrifuge experiments and modelling

Understanding xylem embolism formation is challenging due to dynamic changes and multiphase interactions in conduits. If embolism spread involves gas movement in xylem, we hypothesise that it is affected by time. We measured hydraulic conductivity (K h ) in flow-centrifuge experiments over one hour at a given pressure and temperature for stem samples of three angiosperm species. Temporal changes in K h at 5, 22, and 35°C, and at various pressures were compared to modelled gas pressure changes in a recently embolised vessel in the centre of a centrifuge sample. Temporal changes in K h at 22°C showed maximum relative increases between 6% and 40%, and maximum decreases between 41% and 61% at low and high centrifugal speed, respectively. Logarithmic changes in K h were species-specific, and most pronounced during the first 15 minutes. Embolism formation started near the edges of centrifuge samples and gradually increased at the centre. Moreover, measured decreases in K h strongly correlated with modelled increases in gas concentration in a recently embolised vessel. Although embolism is mostly pressure-driven, our experimental and modelled data indicate that time, conduit characteristics, and temperature are involved due to their role in gas diffusion. Gas diffusion, however, does not cover the entire process of embolism spread.