Salt Regulation in the Mangroves Rhizophora Mucronata Lam. And Aegialitis Annulata Rbr

Abstract

The mangrove Rhizophora mucronata grows in an intertidal region and exchfdes salt from its xylem (17 m·equiv. chloride per litre of sap) more efficiently than does the salt· secreting mangrove AegialitiB annulata (85-122 m·equiv. chloride per litre of sap). From the transpiration stream each leaf of Rhizophora receives about 17 p.·equiv. chloride each day, but the chloride concentration of the growing leaf remains approximately constant (510-560 m·equiv. chloride per litre of sap water). In Aegialiti8 input of chloride to a mature leaf is about 100 p..equiv. per day and this input is balanced by secretion (mainly of sodium chloride) from the salt glands. Secretion collected under oil contains chloride, 450 p.-equiv/ml, sodium, 355 p.-equiv/ ml, and potassium, 27 p.-equiv/ml. Secretion rates from leaves on the tree, based on leaf area, vary from 93 p-equiv. cm-2 sec-1 during the day to 3 p-equiv. cm-2 sec-1 in darkness; the secretion in light, based on an effective gland area, is about 25,000 p-equiv. cm-2 sec-I. The water potential of the secretion is close to that in the leaf suggesting that secretion involves active transport of salt and passive movement of water by local osmosis.