Adjustments in leaf water relations of mangrove (Avicennia germinans) seedlings grown in a salinity gradient

Abstract

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.