Variations in transpiration rate and leaf cell turgor maintenance in saplings of deciduous broad-leaved tree species common in cool temperate forests in Japan

To clarify mechanisms underlying variation in transpiration rate among deciduous broad-leaved tree species, we measured diurnal changes in stomatal conductance (g s ) and leaf water potential, and calculated the maximum transpiration rate (E max ), leaf-specific hydraulic conductance (K s-l ) and difference between the soil water potential and the daily minimum leaf water potential (Ψ s - Ψ l,min ). Pressure-volume (P-V) measurements were made on leaves. Saplings of eight broad-leaved tree species that are common in Japanese cool temperate forests were studied. Maximum transpiration rate varied significantly among species. There was a statistically significant difference in Ψ s - Ψ l,min , but not in K s-l . Species with large E max also had large Ψ s - Ψ l,min and g s . The results of the P-V analyses showed that species with a large Ψ s - Ψ l,min maintained turgor even at low leaf water potentials. The similar daily minimum leaf pressure potentials (Ψ p ) across all eight species indicate that Ψ p values below this minimum are critical. Based on these results, we suggest that the leaf cell capacity for turgor maintenance strongly affects Ψ s - Ψ l,min and consequently E max via stomatal regulation.