Stomatal closure during leaf dehydration, correlation with other leaf physiological traits

Abstract

The question as to what triggers stomatal closure during leaf desiccation remains controversial. This paper examines characteristics of the vascular and photosynthetic functions of the leaf to determine which responds most similarly to stomata during desiccation. Leaf hydraulic conductance (K(leaf)) was measured from the relaxation kinetics of leaf water potential (Psi(l)), and a novel application of this technique allowed the response of K(leaf) to Psi(l) to be determined. These "vulnerability curves" show that K(leaf) is highly sensitive to Psi(l) and that the response of stomatal conductance to Psi(l) is closely correlated with the response of K(leaf) to Psi(l). The turgor loss point of leaves was also correlated with K(leaf) and stomatal closure, whereas the decline in PSII quantum yield during leaf drying occurred at a lower Psi(l) than stomatal closure. These results indicate that stomatal closure is primarily coordinated with K(leaf). However, the close proximity of Psi(l) at initial stomatal closure and initial loss of K(leaf) suggest that partial loss of K(leaf) might occur regularly, presumably necessitating repair of embolisms.

Figure 1.

The two-phase function fitted to pressure volume data for five Gliricidia sepium leaves. Leaf capacitance (C_leaf) was calculated from the slope of the relationship between leaf RWC and Ψ_l (see “Materials and Methods”). Low C_leaf was found in all species before the turgor loss point (dotted line). Post turgor loss, C_leaf increased substantially.

Figure 2.

The relationship between Ψ_l and g_s in evergreen (S. glauca and Q. oleoides) and deciduous (R. trinervis and Gliricidia sepium) species. Data were collected from six trees of each species on sunny days. A range of Ψ_l was measured by surveying g_s under different evaporative conditions. Minimum g_s was measured on detached branches. Curves are cumulative normal distributions.

Figure 3.

Typical rehydration kinetics for S. glauca leaves. Single points represent Ψ_l of leaflets during rehydration of a single compound leaf. All curves are exponential, and the slope is used to calculate K_leaf.

Figure 4.

Response of K_leaf to Ψ_l in each of the four species studied. Each point represents the average K_leaf from two leaves per branch, and a cumulative normal distribution curve is fitted to the data. Dotted lines indicate the Ψ_l at 80% and 20% of maximum g_s, and the heavy dotted line shows the Ψ_l at turgor loss.

Figure 5.

Decreasing quantum yield of PSII during leaf desiccation of detached branches. Each point represents the means ± sd of three to five leaves. Curves are cumulative normal distributions, and dotted lines indicate the Ψ_l at 80% and 20% of maximum g_s.