How Mangroves Desalinate Seawater

Abstract

Abstract Water relations of a number of mangroves and other halophytes were studied. All mangroves had high negative pressure in the xylem (30 to 60 atm) which more than balances the osmotic pressure of the seawater (25 atm). Freezing a short stem section of an attached twig always resulted in wilting caused by eavitation of the tensile sap. Semipemeable membranes in the leaves remained functioning in spite of being iced or healed (50°C), or being poisoned by dinitrophenol and carbon monoxide (13 atm). Chloroform and ether ruptured the membranes. When some 40 atm pressure was applied to the root system of a decapitated seedling potted in seawater, a flow of nearly fresh water ensued. This separation kept on for hours in spile of chilling and poisoning with dinitrophenol or 20 atm carbon monoxide. A reversal of the gradient made roots lose water to the seawater. One may conclude, therefore, that mangroves separate fresh water from the sea by a simple non‐metabolic ultrafiltration process, in a system where high tension obtains in the xylem and where turgor of the living cells is produced by an active maintenance of high solute pressure.