抄録
Plant organs contain large amounts of water. An essential role of water is in maintenance of their internal enviromental conditions where cell growth and physiological functions proceed normally. Plant water stress or water deficit develops when water loss exceeds water absorption due to excessive loss of water, inadequate absorption or a combination of the two. Water stress affects plant growth, modifying morphology, physiology and biochemistry. How much of the water stress are dependent on the degree of the decrease in water potentials, on the processes in physiology, on the growth stages and on the kinds of plants. Osmotic adjustment contributes to the maintenance of turgor for keeping normal plant growth processes. Osmotic adjustment refers to a net increase in solute, as distinguished from the passive increase in the concentration caused by loss of water. We examined the degree of osmotic adjustment in the mangroves, Rhyzophora stylosa Griff, and Bruguiera gymnorrhiza (L.) Lamk., in the area from sea water along the coast to brackish water in the mouth of the river. From these examinations we found that the mangrove trees growing in sea water and brackish water areas maintained high turgor potentials due to osmotic adjustment and that the mangrove trees growing in sea water area along the coast were probably absorbing water with higher water potential than that of sea water. However, the small and young tree directly absorbing sea water could not maintain high turgor potential due to insufficient osmotic adjustmet. Therefore, we suggest that this tree would suffer from water stress under intense transpiration condition on fine day.
