title: Hydrogen isotope response to changing salinity and rainfall in Australian mangroves.
abstract: Hydrogen isotope ratios ((2) H/(1) H, δ(2) H) of leaf waxes covary with those in precipitation and are therefore a useful paleohydrologic proxy. Mangroves are an exception to this relationship because their δ(2) H values are also influenced by salinity. The mechanisms underlying this response were investigated by measuring leaf lipid δ(2) H and leaf and xylem water δ(2) H and δ(18) O values from three mangrove species over 9.5 months in a subtropical Australian estuary. Net (2) H/(1) H fractionation between surface water and leaf lipids decreased by 0.5-1.0‰ ppt(-1) for n-alkanes and 0.4-0.8‰ ppt(-1) for isoprenoids. Xylem water was (2) H depleted relative to surface water, reflecting (2) H discrimination of 4-10‰ during water uptake at all salinities and opportunistic uptake of freshwater at high salinity. However, leaf water (2) H enrichment relative to estuary water was insensitive to salinity and identical for all species. Therefore, variations in leaf and xylem water δ(2) H values cannot explain the salinity-dependent (2) H depletion in leaf lipids, nor the 30‰ range in leaf lipid δ(2) H values among species. Biochemical changes in direct response to salt stress, such as increased compatible solute production or preferential use of stored carbohydrates, and/or the timing of lipid production and subsequent turnover rates, are more likely causes.
authors.affiliation: School of Oceanography, University of Washington, Box 355315, Seattle, WA, 98195, USA. Nemiah.Ladd@eawag.ch.
authors.forename: S Nemiah
authors.initials: SN
authors.lastname: Ladd
authors.affiliation: School of Oceanography, University of Washington, Box 355315, Seattle, WA, 98195, USA.
authors.forename: Julian P
authors.initials: JP
authors.lastname: Sachs
mesh_terms: D032407:Avicennia / Q000378:metabolism*; D003903:Deuterium / Q000032:analysis; D006859:Hydrogen / Q000378:metabolism*; D010103:Oxygen Isotopes / Q000032:analysis; D018515:Plant Leaves / Q000378:metabolism; D011891:Rain; D043982:Rhizophoraceae / Q000378:metabolism*; D054712:Salinity; D014867:Water / Q000378:metabolism*; D052584:Xylem / Q000378:metabolism
chemical_list: D010103:Oxygen Isotopes; D014867:Water; D006859:Hydrogen; D003903:Deuterium
keywords: leaf waxes; paleoclimate; taraxerol; water relations