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Physiological Section

Paredes López, Claudia [1], Lopez-Portillo, Jorge [2].

Is there predawn disequilibrium between plant and soil water potentials in the mangrove Laguncularia racemosa?

Predawn disequilibrium is defined as the imbalance between the soil and the plant water potentials, because both are supposed to be similar if stomates close and there is enough time for overnight equilibrium. In this context, mangrove trees are interesting models to study this phenomenon because they grow under and ample salinity range, and the difference between soil and plant may be very evident. Also, because their roots are relatively shallow and are frequently flooded, thus having a homogeneous environment. By measuring soil water potentials, and plant pressure and xylem osmotic potentials, we experimentally determined the magnitude of predawn disequilibrium and tested the contribution of nighttime transpiration by bagging (and keeping unbagged controls of) 18 month old Laguncularia racemosa plants grown under four salinity concentrations which corresponded to 0, 0.9, 1.8 and 3.6 MPa, but flooded at all times (water being at 2 cm above soil level). A significant predawn disequilibrium was found in all treatments. Furthermore, there was a significantly greater disequilibrium in unbagged plants only with the lower substrate salinity treatments (0 and 0.9 MPa), and the contribution of the xylem osmotic potential increased with substrate salinity. Our results indicate that although the magnitude of disequilibrium is related to the substrate salinity, the water potential in this mangrove never equilibrates with that of the soil. As we have ruled out the root environment and night transpiration as sources of the disequilibrium, it remains to be tested whether there is a high capacitance in the plant, or low hydraulic conductance that may increase the time needed to reach overnight equilibrium.

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1 - Institutuo de Ecologia, A.C., Ecologia Funcional, km 2.5 antigua carretera a Coatepec No. 351, Congregación El Haya, Xalapa, Veracruz, 91070, México
2 - Instituto de Ecología, A. C., Departamento Ecología Vegetal, km 2.5 antigua carretera a Coatepec No. 351, Congregación El Haya, Xalapa, Veracruz, 91070, Mexico

Nighttime transpiration
Laguncularia racemosa
Osmotic potential
Pressure potential.

Presentation Type: Poster
Session: 33-71
Location: Salon C, D & E - Gov Ballroom/Hilton
Date: Tuesday, August 16th, 2005
Time: 12:30 PM
Abstract ID:165

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