© 2000 Heron Publishing—Victoria, Canada
Adjustments in leaf water relations of mangrove (Avicennia germinans) seedlings grown in a salinity gradient
N. Suárez (1, 2) and M. A. Sobrado (1, 3)
1. Laboratorio de Biología Ambiental de Plantas, Departamento de Biología de Organismos, Universidad Simón Bolívar, Apartado
89.000, Caracas 1080A Venezuela / 2. Ecología, IVIC, Apartado 21827. Caracas, Venezuela / 3. Author to whom correspondence should be addressed (msobrado@skynet.usb.ve) / Received September 30, 1998
Summary
We used pressure–volume analysis and dewpoint hygrometry to determine leaf water relation parameters of mangrove (Avicennia germinans L.) seedlings grown at salinities of 0, 8, 20 and 32 ‰. Seedlings responded to an increase in salinity from 0 to 32 ‰ by
an increase in leaf succulence as reflected in an increase in leaf water content per unit area from 300 to 360 g m–2. Additionally, osmotic potential at full turgor decreased from –2.3 to –3.5 MPa and osmotic potential at zero turgor decreased
from –2.7 to –4.3 MPa. Cell elasticity decreased as salinity increased from 0 to 32 ‰, as indicated by a progressive increase
in volumetric modulus of elasticity from 19 to 27 MPa. Increased leaf succulence enabled leaves to sequester large amounts
of solutes without adversely increasing cell osmotic pressure. On the other hand, osmotic adjustment facilitated turgor maintenance
as water potential diminished. Salinity-induced decreases in tissue elasticity generated greater water potential differences
between leaves and soil under saline conditions than under non-saline conditions.
Keywords:
elasticity, halophyte, osmotic potential, succulence, turgor pressure, water content.
