title: Osmotic and hydraulic adjustment of mangrove saplings to extreme salinity.
abstract: Salinity tolerance in plant species varies widely due to adaptation and acclimation processes at the cellular and whole-plant scales. In mangroves, extreme substrate salinity induces hydraulic failure and ion excess toxicity and reduces growth and survival, thus suggesting a potentially critical role for physiological acclimation to salinity. We tested the hypothesis that osmotic adjustment, a key type of plasticity that mitigates salinity shock, would take place in coordination with declines in whole-plant hydraulic conductance in a common garden experiment using saplings of three mangrove species with different salinity tolerances (Avicennia germinans L., Rhizophora mangle L. and Laguncularia racemosa (L.) C.F. Gaertn., ordered from higher to lower salinity tolerance). For each mangrove species, four salinity treatments (1, 10, 30 and 50 practical salinity units) were established and the time trajectories were determined for leaf osmotic potential (Ψs), stomatal conductance (gs), whole-plant hydraulic conductance (Kplant) and predawn disequilibrium between xylem and substrate water potentials (Ψpdd). We expected that, for all three species, salinity increments would result in coordinated declines in Ψs, gsand Kplant, and that the Ψpddwould increase with substrate salinity and time of exposure. In concordance with our predictions, reductions in substrate water potential promoted a coordinated decline in Ψs, gsand Kplant, whereas the Ψpddincreased substantially during the first 4 days but dissipated after 7 days, indicating a time lag for equilibration after a change in substratum salinity. Our results show that mangroves confront and partially ameliorate acute salinity stress via simultaneous reductions in Ψs, gsand Kplant, thus developing synergistic physiological responses at the cell and whole-plant scales.
authors: Departamento de Biología de la Conservación, Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE), Carretera Ensenada-Tijuana No. 3918, Zona Playitas, Ensenada, B.C., 22860, México mendezal@cicese.mx.
authors: Rodrigo
authors: R
authors: Méndez-Alonzo
authors: Red de Ecología Funcional, Instituto de Ecología, A.C., Xalapa, Veracruz, 91070, México.
authors: Jorge
authors: J
authors: López-Portillo
authors: Instituto de Investigaciones en Ecosistemas y Sustentabilidad, Universidad Nacional Autónoma de México, Morelia, Michoacán, 58190 , México.
authors: Coral
authors: C
authors: Moctezuma
authors: Department of Ecology and Evolutionary Biology, University of California Los Angeles, Los Angeles, CA 90095-1606, USA.
authors: Megan K
authors: MK
authors: Bartlett
authors: Department of Ecology and Evolutionary Biology, University of California Los Angeles, Los Angeles, CA 90095-1606, USA.
authors: Lawren
authors: L
authors: Sack
mesh_terms: D000222:Adaptation, Physiological; D032407:Avicennia / Q000502:physiology*; D029764:Combretaceae / Q000502:physiology*; D009997:Osmotic Pressure; D043982:Rhizophoraceae / Q000502:physiology*; D054712:Salinity; D055051:Salt-Tolerant Plants; D014867:Water; D053833:Wetlands
chemical_list: D014867:Water
keywords: Mexico; mangroves; plant turgor; predawn disequilibrium; salinity stress; saplings; stomatal conductance