Abstract Detail

Physiological Section

Lopez-Portillo, Jorge [1], Ewers, Frank W. [2], Angeles, Guillermo [3].

Sap salinity effects on xylem conductivity in two mangrove species.

Xylem sap salinity and conductivity were examined in two mangrove ecosystem tree species. For Avicennia germinans, extracted xylem sap osmotic potentials ranged from -0.24 to -1.36 MPa vs. -0.14 to -0.56 MPa for Conocapus erectus. Xylem sap of Conocapus did not vary in osmotic potential between sites nor between predawn and midday. In Avicennia, values were more negative at midday than predawn, and also more negative at hypersaline than hyposaline sites. After removing embolisms, specific conductivity (K_s) was measured as a function of salinity of the artificial xylem sap perfusion. For both species the lowest K_s values, about 70% of the maximum K_s, were obtained when stems were perfused with deionized water (0 mM; 0.0 MPa) or with a 557 mM saline solution (-2.4 MPa). Higher Ks values were obtained in the range from -0.3 to -1.2 MPa, with a peak at -0.82 ± 0.08 MPa for Avicennia and -0.75 ± 0.08 MPa for Conocarpus. The variations in K_s values with minima both at very low and very high salt concentrations were consistent with published results for swelling and shrinking of synthetic hydrogels, suggesting native hydrogels in pit membranes of vessels could help regulate conductivity.