Surface rehydration kinetics
In both species, leaf exposure to artificial fog led to full leaf
rehydration via FWU across all treatments (Figure 3). Leaf rehydration
kinetics, in terms of gain in mass and Ψ increment over time, was fit
with exponential curves (Table 1 Supporting Information) to calculate
specific components of the absorption process. Based on fit estimates,P. dulcis leaves absorbed between 9.9 to 13.2 g
m-2, and P. communis leaves between 8.5 to 13.5
g m-2 (or ~0.1 g g-1DW in all cases). The Ψ after prolonged rehydration stabilized within
-0.4 to -0.7 MPa in P. dulcis and -0.3 to -0.7 MPa in P.
communis .
In all treatments, abaxially sealed P. dulcis leaves absorbed the
about same amount of water through their adaxial stomata-free surface
(P =0.873, Table 4
Supporting Information). After approximately 2 hours of fog exposure,
FC, ABA and control leaves had respectively absorbed 2.1 ± 0.3, 2.0 ±
0.3 and 2.2 ± 0.3 g m-2. This suggests that, at least
for this species, treatments did not have a significant influence on the
hydraulic properties of the cuticle and on leaf surface rehydration, so
that differences in the parameters measured in non-sealed leaves can be
distinctly attributed to stomatal apertures. This quantity of water was
approximately half of the water absorbed by non-sealed leaves with
stomata mainly closed (control and ABA treated leaves) after
~2 hours of fog exposure, suggesting that cuticle
permeability of adaxial and abaxial surfaces is similar in P.
dulcis .
In both species, half-times (t50; time at which 50% of
mass and Ψ increments are reached) were significantly shorter for FC
than for ABA treated leaves (Table 1, Figure 3a-d), indicating faster
rehydration and Ψ recovery via FWU in leaves with open stomata.
Similarly, maximum water flux (Qmax) was approximately 3
times greater for FC than for ABA treated leaves of both species (Table
1). Maximum hydraulic conductance (Kmax; inverse of
minimum resistance, Rmin) was 4 and 3 times greater in
FC than ABA treated leaves of P. dulcis and P. communis ,
respectively (Table 1, Figure 3e, f). Both Qmax and
Rmin were reached between 2.3 and 2.7 times faster in FC
than ABA treated leaves (Table 1). At the time of Rmin,
Ψ in P. dulcis was about -0.7 MPa (FC) and -1.1 MPa (both ABA and
control), and about -1.1 MPa in P. communis (all treatments),
which represents a respective Ψ decrease of about 63%, 35% and 42%
relative to initial Ψ values. Despite the remarkably higher
gs of P. communis ABA and control leaves compared
to that of P. dulcis , the FWU rate (Qmax) was
similar in both species. In contrast, similar gs values
were attained by FC leaves of both species, but the FWU rate in P.
communis was only half of that recorded in P. dulcis (Table 1).