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).