Analysis of Pressure-Volume Curves of Leaves of Rosa hybrida cv. Sonia

By analysing the relationship between inverse water potential (ψ−1), and relative water content (RWC) measured on leaves of roses (Rosa hybrida cv. Sonia), grown soilless, it was found that a non-linear (NL) model was better suited than a linear model to reproduce values observed in the non-turgid region. To explain this apparent curvature, it is assumed that a reduction of the non-osmotic water fraction (Ap) takes place when ψ decreases. Osmotic potentials (ψπ) measured on fresh and frozen leaf discs tend to support this hypothesis. A method for exploiting PV curves, which takes into account the variation of Ap, is described. It delivers values for the turgor pressure (πp), the relative osmotic water content, and the mean bulk volumetric elasticity coefficient, lower than those given by the linear model. On the other hand, it gives higher estimates for Ap and for ψπ. When applying the traditional model to obtain estimates for water relations characteristics of rose leaves, and comparing results from two distinct salinity treatments (electrical conductivities of 1·8 mS cm−1 and 3·8 mS cm−1, respectively), one deduces a significant reduction of ψπ at turgor-loss in the high salinity treatment. The NL method is, in addition, able simultaneously to reveal a reduction of ψπ and a significant increase in ψp at RWC=100% this proves that soilless-grown rose plants are able to osmoregulate when subjected to a constant and relatively high degree of salinity.