(1)
Reversible changes in bark thickness depend on three processes. First,
changes in bark hydraulic capacitance (component 1), expressed by the
symbol D bΨP,x in the text;
second, changes in bark osmotic concentration (component 2) caused by
lateral solute fluxes, i.e.D bΨΠ,b; third, xylem conduit
diameter response to xylem tension (component 3), i.e.D xΨP,x. The first two processes
are driven by the radial fluxes, respectively, of water and solutes to
and from the xylem into the bark. The third component is the result of a
balancing act between soil water availability, atmospheric dryness and
stomatal regulation of water loss at the leaf. Component 1 in Eqn. (1)
is derived from Mencuccini et al. (2013). Therefore, the term
marked as component 2 in Eqn. (1) above gives the net fraction of the
changes in bark osmotic concentration that depends directly on the
corresponding changes in xylem osmotic concentration. α, β and γ are
defined as in Mencuccini et al. (2017):