Ewers, Frank W. , Paredes, C. , Lopez-Portillo, Jorge , Angeles, Guillermo .
The salinity of xylem sap in mangrove trees.
Mangrove trees and other halophytes are usually reported to have high concentrations of salts in their xylem sap, but other reports indicate the sap is close to pure water, similar to the situation in glycophytes. Here we explored whether the vacuum extraction technique and the pressure chamber technique lead to similar results and examined also possible artifacts. Using a pressure chamber on twigs, the osmolarity of successive 10 microliter drops of xylem sap were measured, followed by extraction of 150 microliter samples. The twig stumps were then re-cut and re-sampled several times to test for possible contamination. Using the pressure chamber, the first drops extracted had osmolarities of about 700 mmol for Avicennina germinans versus about 100 mmol for Laguncularia racemosa. Successive drops had lower osmolarities, and 150 microliter extractions had still lower osmolarities of 50 mmol or less. Re-cuts had little or no impact on osmolarity. However, when stems were initially cut under deionized water rather than in open air, in some cases there was slightly lower measured osmolarity, suggesting less contamination when stems were cut in air. The vacuum extraction method was used to collect successive samples from debarked one meter long stems 10 to 15 mm in diameter. The successive samples gave results consistently similar to the first or second drop extracted with the pressure chamber method. The results imply that the first and second drops extracted with the pressure chamber method give an accurate measurement of intact xylem sap, whereas continued extraction results gave artificially low measured salinity, probably due to reverse osmosis. Both mangroves had much higher sap salinities than reported in glycophytes. Results are consistent with the interpretation by Scholander and others of Avicennia as a salt excreter with very high sap salinity, and Laguncularia as a salt excluder with lower sap salinity.
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1 - Biological Sciences Department, California State Polytechnic University, Pomona, CA, USA
2 - Instituto de Ecologia, A.C., Xalapa, Veracruz, Mexico
Presentation Type: Oral Paper:Papers for BSA Sections
Location: Wasatch B/Cliff Lodge - Level C
Date: Tuesday, July 28th, 2009
Time: 11:15 AM