Dynamics of element contents during the development of hypocotyles and leaves of certain mangrove species

The changes in the contents of chlorine, sodium, potassium, calcium, magnesium and ash have been investigated during the development of the leaves of eight mangrove species: Kandelia candel Druce, Bruguiera gymnorrhiza Lamk., B. sexangula Poir., Rhizophora stylosa Griff., R. apiculata Blume, Ceriops tagal C.B. Rob., Aegiceras corniculatum Blanco and Avicennia marina Vierh., and the viviparous hypocotyles of K. candel, B. gymnorrhiza and B. sexangula in China. With the in situ viviparous development of hypocotyle, contents of chlorine, sodium, potassium, calcium, magnesium and ash in the hypocotyle decreased, indicating that the development of hypocotyle is not a salt-accumulating process, but a desalinating process. With the development of the leaves from young to old, the content of potassium decreased, while calcium and magnesium increased both in salt-secretors and salt-nonsecretors. Sodium, chlorine and ash increased in salt-nonsecretors and decreased in salt-secretors. Eliminating excessive salt by loss of old leaves that are rich in salt is one of the characteristics by which salt-nonsecretors adapt themselves to saline environments. Potassium can be reabsorbed from senescing leaves and reused for the growth of new organs.