Salt balance of leaves of the mangrove Avicennia marina

The contribution of each of the salt‐transporting processes to the NaCl balance of the leaves of the salt‐recreting mangrove Avicennia marina (Forssk.) Vierh. was quantitatively investigated. Transpiration rates, xylem sap concentration, leaf salt content, recretion rates and rates of salt retranslocation out of the leaves were continuously monitored during three day periods and the salt fluxes in and out of the leaves were calculated. The results indicated that salt filtration by the roots is by far the most important salt‐rejecting mechanism, preventing some 80% of the salt which is carried towards the root surface by the transpiration stream, from entering the shoot. Out of the remaining quantity of salts which enter the root xylem and reach the leaves, only 40% is removed by the salt‐recreting glands.