Estimation of water potential components and pressure-volume curve parameters - Goetz Program Recap

Osmotic and turgor water potentials are the principal components of a global potential term; they are usually measured by pressure methods in vegetative organs, like leaves or pieces of shoot. Considering that the components of plant water potential have opposite sign (negative for osmotic and positive for turgor water potential), the simple measurement of total water potential does not provide any information about its components. To this aim, is therefore necessary to plot, together with the Pressure–Volume (P- V) curve, the components of leaf water potential versus leaf water contents. In the literature, this kind of plot is known as “Höfler diagram” (Richter, 1978), . The knowledge of the P-V curve, allows to identify specific parameters (turgor loss point and osmotic potential at saturation) indicating the drought tolerance of a certain vegetation species. Moreover, volumetric bulk elastic modulus, reflecting the mechanical propertied of cell walls, can be mathematically derived. Proximal spectral reflectance in the visible, near-infrared, and shortwave-infrared (VIS–NIR–SWIR) regions (350–2500 nm) have been successfully used for an accurate and rapid estimation of vegetation water status, as well as of biochemical and bio-agronomic properties involved into important physiological processes such as water exchange, photosynthesis, biochemistry of plant pigments, etc. Estimation of energy status of water in vegetative organs via proximal spectral reflectance is a convenient and rapid field-scale measurement approach, although it is applicable only to characterize the vegetation surface. Despite several field and laboratory experimental studies have been investigated the interactions between energy and water status, a poor scientific focus has been aimed to study the intrinsic interaction between the energy and the elementary components of the vegetation water potential, as well as the relationship between the energy and the mechanical properties of the cell walls. Only a research carried out by Peñuelas et al. (1993) presented some considerations about the effects of volumetric elastic module parameter on the reflectance response of gerbera plants. However, this study did not include the parametric approach to estimate the behavior of vegetative organs expressed in terms of Pressure-Volume curve. Considering that the proximal spectral reflectance signatures contains information about vegetation water status and biomass structure, it can be assumed that the parameters describing the P-V patterns should be related to the vegetation spectral response.