Effect of high external NaCl concentration on the osmolality of xylem sap, leaf tissue and leaf glands secretion of the mangrove Avicennia germinans (L.) L.
Abstract
The relative changes in osmolality of leaf tissue, xylem sap and leaf secretion, as well as leaf gas exchange characteristics of the mangrove A. germinans, cultivated under moderate salinity (0 to 428mol NaCl m‑3) and hypersaline conditions (856mol NaCl m‑3), were examined. Water content and net amount of solutes per unit leaf area increased at moderate salinity, and then declined under hypersalinity. Osmolality of xylem sap increased with salinity treatment in actively transpiring plants as well as at night when transpiration was minimized. However, osmolality values of salt-treated plants were higher at night than during the day, which indicated the dependence of this parameter on water flow. At moderate salinity, salt secretion increased with salinity treatment. This allowed plants to reduce water uptake slightly and to maintain relatively high carbon assimilation. However, under hypersaline conditions, salt secretion tended to be limited, which may be the result of a saturated process. Salt secretion is a highly active mechanism and involves several metabolically controlled steps. Therefore, in hypersaline conditions, decreases in the solutes carried to leaves were more important. Thus, stomatal conductance of A. germinans was severely reduced. However, this lead also to a drastic reduction in carbon assimilation rates.
- Publication:
-
Flora: Morphology, Distribution, Functional Ecology of Plants
- Pub Date:
- January 2001
- DOI:
- 10.1016/S0367-2530(17)30013-0
- Bibcode:
- 2001FMDFE.196...63S
- Keywords:
-
- osmotic potential;
- photosynthesis;
- salinity;
- salt secretion;
- transpiration;
- water relations