WATER-BALANCE IN THE ARBORESCENT PALM, SABAL-PALMETTO .1. STEM STRUCTURE, TISSUE WATER RELEASE PROPERTIES AND LEAF EPIDERMAL CONDUCTANCE

The functional importance of water storage in the arborescent palm, Sabal palmetto, was investigated by observing aboveground water content, pressure-volume curve parameters of leaf and stem tissue and leaf epidermal conductance rates. The ratio of the amount of water stored within the stem to the leaf area (kg m-2) increased linearly with plant height. Pressure-volume curves for leaf and stem parenchyma differed markedly; leaves lost turgor at 0.90 relative water content and -3.81 MPa, while the turgor loss point for stem parenchyma occurred at 0.64 relative water content and -0.96 MPa. Specific capacitance (change in relative water content per change in tissue water potential) of stem parenchyma tissue was 84 times higher than that of leaves, while the bulk modulus of elasticity was 346 times lower. Leaf epidermal conductance rates were extremely low (0.32-0.56 mmol m-2 s-1) suggesting that S. palmetto are able to strongly restrict foliar water loss rates. Structurally, stems of S. palmetto appear to be well suited to act as a water storage reservoir, and coupled with the ability to restrict water loss from leaf surfaces, may play an important role in tree survival during periods of low water availability.