Comparison between two methods of generating pressure-volume curves in Quercus species

Abstract

Water relation parameters derived from the pressure-volume curves of eight Quercus species from contrasting phytoclimates: Mediterranean (Q. coccifera L., Q. ilex ssp. ballota L. and Q. suber L.), nemoral (Q. laurifolia Michx. and Q. rubra L.) and nemoro-Mediterranean (Q. cerris L., Q. faginea Lam. and Q. pyrenaica Willd.), were compared using the sap expression (SE) and free transpiration techniques (TL). The methods yield different results for the relative simplasmic water content (S) in all species, and the same results for the relative simplasmic water expressed at the turgor loss point (Sptt) and the maximum bulk modulus of elasticity (εmax) in all species with the exception of Q. pyrenaica Nemoral species showed similar results in all P-V parameters with both techniques, except for S. Most of the Mediterranean species (Q. coccifera and Q. ilex) showed differences in all the studied parameters, except for εmax and Sptt. Nemoro-Mediterranean species behaved differently, Q. cerris behaved like the Mediterranean species and Q. faginea like the nemoral species, for all the hydric parameters. The more negative values in osmotic potential at full turgor (Π0) water potential at the turgor loss point (ψppt) and the higher values of S in the more sclerophyllous species, pointed to ppt a tendency to get a shallower slope with the TL method. These disagreements did not allow a similar arrangement of the species according to the P-V curves parameters.