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.