problems of salt water
Plants experience many problems living in or near sea water which is 'physiologically dry' because most plant and animal tissues are more dilute than seawater. For osmosis to occur, water must move from a more dilute to a more concentrated compartment. This is why when one waters a normal plant with sea water, the plant will wither and die as the salty soil now extracts water from the plant instead of replenishing it!
Some mangrove plants like Api-api (Avicennia species), Jeruju (Acanthus species) or Kacang-kacang (Aegiceras corniculata) are salt secretors. The common salt concentration in the sap is high at about one-tenth that of sea water. Salt is partially excluded by the roots and the salt is excreted by the salt glands by the plant expending energy.
Other mangrove plants like Bruguiera, Lumnitzera, Rhizophora or Sonneratia species are non-secretors. They can selectively absorb only certain ions (electrically charged atom(s) andlor group of atom(s) which a salt becomes on going into solution) from the solutions they come into contact with by a process called ultrafiltration. However, even with this, exclusion is not complete. Some salt is lost by transpiration through the leaf surface or accumulates in some cells of the leaf. Suggestions have even been made that some species deposit a good part of the excess salts in the old leaves which are shed.
Other adaptations to cope in the mangroves:
From "A Guide to Mangroves of Singapore", Peter K. L. Ng and N. Sivasothi (editors)
Volume 1: The Ecosystem and Plant Diversity and Volume 2: Animal Diversity
Authors: Kelvin K. P. Lim, Dennis H. Murphy, T. Morgany, N. Sivasothi, Peter K. L. Ng,
B. C. Soong, Hugh T. W. Tan, K. S. Tan & T. K. Tan
BP Guide to Nature Series published by the Singapore Science Centre, sponsored by British Petroleum
© 2001 Raffles Museum of Biodiversity Research, The National University of Singapore & The Singapore Science Centre