Stomatal conductance of dehydrating leaves
The effect of the chemical treatments on the stomatal conductance
(gs) of leaves was assessed in relation to Ψ as measured
by balancing pressure. We used 24 randomly selected leaves of P.
dulcis (10 FC, 7 ABA, 7 control) and 20 leaves of P. communis (7
FC, 6 ABA, 7 control). For each leaf, gs was measured
periodically during dehydration (from Ψ close to zero to turgor loss
point) using a portable photosynthesis system (LI-6400, Li-Cor, Lincoln,
NE, USA) in darkness, with an air flow of 1,000 μmol
s−1 and RH set at 70%. The Ψ was recorded after each
gs measurement. Initial trials showed that at room
conditions, leaves – especially FC treated leaves – dehydrated rather
fast, limiting the number of measurements that could be performed when
still turgid. Thus, to reduce the speed of dehydration, leaves were kept
in dark, small containers filled with wet paper towels between
measurements. The relationship between gs and Ψ was
assessed by fitting data to a linear mixed-effect model with treatment
as fixed factor and leaf as random factor. Data were compared at the
average Ψ value (least-square mean) predicted for all the treatments and
both species using analysis of variance (ANOVA) and Tukey tests. The
model was also used to estimate gs at Ψ values when
maximum flux (Qmax) and maximum hydraulic conductance
(Kmax) were reached and evaluate potential correlations.
Statistical analyses were performed with R (v.3.5.1, the R Foundation
for Statistical Computing, Vienna, Austria).