title: Dynamic control of osmolality and ionic composition of the xylem sap in two mangrove species.
abstract: • Premise of the study: Xylem sap osmolality and salinity is a critical unresolved issue in plant function with impacts on transport efficiency, pressure gradients, and living cell turgor pressure, especially for halophytes such as mangrove trees.• Methods: We collected successive xylem vessel sap samples from stems and shoots of Avicennia germinans and Laguncularia racemosa using vacuum and pressure extraction and measured their osmolality. Following a series of extractions with the pressure chamber, we depressurized the shoot and pressurized again after various equilibration periods (minutes to hours) to test for dynamic control of osmolality. Transpiration and final sap osmolality were measured in shoots perfused with deionized water or different seawater dilutions.• Key results: For both species, the sap osmolality values of consecutive samples collected by vacuum extraction were stable and matched those of the initial samples extracted with the pressure chamber. Further extraction of samples with the pressure chamber decreased sap osmolality, suggesting reverse osmosis occurred. However, sap osmolalities increased when longer equilibration periods after sap extraction were allowed. Analysis of expressed sap with HPLC indicated a 1:1 relation between measured osmolality and the osmolality of the inorganic ions in the sap (mainly Na+, K+, and Cl-), suggesting no contamination by organic compounds. In stems perfused with deionized water, the sap osmolality increased to mimic the native sap osmolality.• Conclusions: Xylem sap osmolality and ionic contents are dynamically adjusted by mangroves and may help modulate turgor pressure, hydraulic conductivity, and water potential, thus being important for mangrove physiology, survival, and distribution.
authors.affiliation: Red de Ecología Funcional, Instituto de Ecología, A. C., Carretera antigua a Coatepec 351 El Haya Xalapa 91070 Veracruz, México.
authors.forename: Jorge
authors.initials: J
authors.lastname: López-Portillo
authors.affiliation: Biological Sciences Department, California State Polytechnic University, Pomona, 3801 West Temple Avenue, Pomona, California 91768 USA.
authors.forename: Frank W
authors.initials: FW
authors.lastname: Ewers
authors.affiliation: Red de Ecología Funcional, Instituto de Ecología, A. C., Carretera antigua a Coatepec 351 El Haya Xalapa 91070 Veracruz, México.
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Méndez-Alonzo
authors.affiliation: Posgrado en Ecología y Manejo de Recursos, Instituto de Ecología, A. C. Carretera antigua a Coatepec 351 El Haya Xalapa 91070 Veracruz, México.
authors.forename: Claudia L
authors.initials: CL
authors.lastname: Paredes López
authors.affiliation: Red de Ecología Funcional, Instituto de Ecología, A. C., Carretera antigua a Coatepec 351 El Haya Xalapa 91070 Veracruz, México.
authors.forename: Guillermo
authors.initials: G
authors.lastname: Angeles
authors.affiliation: Centro de Ciencias de la Atmósfera, UNAM, Circuito Exterior, Ciudad Universitaria, México, D.F. 14510 México.
authors.forename: Ana Luisa
authors.initials: AL
authors.lastname: Alarcón Jiménez
authors.affiliation: Red de Ecología Funcional, Instituto de Ecología, A. C., Carretera antigua a Coatepec 351 El Haya Xalapa 91070 Veracruz, México.
authors.forename: Ana Laura
authors.initials: AL
authors.lastname: Lara-Domínguez
authors.affiliation: Centro de Ciencias de la Atmósfera, UNAM, Circuito Exterior, Ciudad Universitaria, México, D.F. 14510 México.
authors.forename: María Del Carmen
authors.initials: MD
authors.lastname: Torres Barrera
mesh_terms: D032407:Avicennia / Q000737:chemistry*; D029764:Combretaceae / Q000737:chemistry*; D009994:Osmolar Concentration; D018526:Plant Transpiration; D054712:Salinity; D055051:Salt-Tolerant Plants / Q000737:chemistry; D014197:Trees; D014867:Water; D052584:Xylem / Q000737:chemistry*
chemical_list: D014867:Water
keywords: Avicennia germinans; Laguncularia racemosa; ion-mediated hydraulic conductivity; mangroves; sap ionic composition; sap salinity; turgor pressure; water potential; xylem sap osmotic potential; xylem sap solutes