Stomatal Closure during Leaf Dehydration, Correlation with Other Leaf Physiological Traits

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 (Kleaf) was measured from the relaxation kinetics of leaf water potential (l), and a novel application of this technique allowed the response of Kleaf to l to be determined. These “vulnerability curves” show that Kleaf is highly sensitive to l and that the response of stomatal conductance to l is closely correlated with the response of Kleaf to l. The turgor loss point of leaves was also correlated with Kleaf and stomatal closure, whereas the decline in PSII quantum yield during leaf drying occurred at a lower l than stomatal closure. These results indicate that stomatal closure is primarily coordinated with Kleaf. However, the close proximity of l at initial stomatal closure and initial loss of Kleaf suggest that partial loss of Kleaf might occur regularly, presumably necessitating repair of embolisms.