AUTECOLOGICAL STUDIES ON AN ESTUARINE PLANT - EFFECTS OF SALINITY ANDFLOODING ON THE GROWTH OF MACHAERIUM-LUNATUS (L) GFW MEY

Growth studies of Machaerium lunatus (L.) G.F.W. Mey, Leguminosae (Fab aceae) were carried out on 4-week old seedlings grown in sand culture at different salinities in both flooded and non-flooded conditions. Gr owth in terms of plant height, dry weight, RGR, NAR and LAR was signif icantly higher at 1% seawater than at higher salinities or in non-sali ne medium. In flooded condition, growth was also best at 1% seawater c oncentration. Leaf succulence, particularly in terms of mesophyll thic kness, increased with increase in salinity. Sodium ion was found to be more effective in stimulating leaf succulence than the chloride ion. The sodium ion salinity effects resembled seawater salinity effects mo re closely than did chloride ion salinity effects in respect of leaf s ucculence, total chlorophyll content and WSD. Seawater and chloride io n have no discernible effect on root/shoot ratio, while the ratio seem ed to decrease as sodium ion salinity increased. The leaf structure wa s modified by the appearance of aerenchymatous of the leaves. The spac es at the adaxial surface of the leaves were greater in size and numbe r at 1 and 10% seawater (salinity 0.34 and 3.43 parts per thousand), t han at any other salinity. Chlorophyll content of leaves was higher at 1% seawater than at any other salinity. However, the chlorophyll cont ent of leaves of flooded seedlings decreased with age at all salinity levels unlike the non-flooded controls. Very low leaf water potentials and high water saturation deficits occurred as salinity increased in both flooded and control seedlings. The plant has been proposed as a f acultative halophyte.