Effect of FC and ABA treatments – ESEM microscopy assessment
ESEM analyses provided direct evidence that treatments modified stomatal aperture (Figure 2). Since ESEM images do not show pore walls as the electron beam is shielded by cuticular ledges, we used the distance (width) between the ledges as a proxy for stomatal pore aperture (Figure 2a, c, d). Treatments significantly influenced stomatal aperture in bothP. dulcis and P. communis (P <0.0001, Table 3 Supporting Information). The width (mean ± se in µm) between ledges was greater in FC leaves (2.53 ± 0.11) than in ABA (0.57 ± 0.10) and control leaves (0.50 ± 0.11) of P. dulcis(P <0.0001; P =0.819 for ABA vs control leaves). In P. communis , FC treated leaves also had the largest pore width (2.07 ± 0.12), followed by control (1.38 ± 0.13) and then ABA (0.83 ± 0.12) treated leaves (P <0.005). Differences in stomatal pore apertures agree with differences in the fluxes recorded, both gmax and Qmax (Figure 1a, b Supporting Information). The density of stomata was 211.5 ± 1.6 and 179.8 ± 2.0 stomata mm-2 in P. dulcis and P. communis , respectively.
Simulated fog conditions by an increase of RH up to 100% in the microscope chamber revealed different stages of water condensation that were affected by time and leaf surface location. Roughly, water first condensed as relatively small droplets onto epidermal furrows among epidermal cell wall folds. These droplets increased in size by further condensation until coalescing, eventually forming films that covered all the furrows. Larger droplets appeared later on top of the folds which were then fully covered by a water film. Up to that point stomata were not covered with water. Further water accumulation resulted in the formation of a water film covering the entire leaf surface.