Tree Physiology Advance Access originally published online on March 11, 2009
Tree Physiology 2009 29(5):697-705; doi:10.1093/treephys/tpp005
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Hydraulic redistribution in dwarf Rhizophora mangle trees driven by interstitial soil water salinity gradients: impacts on hydraulic architecture and gas exchange
1 Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun, Mengla, Yunnan Province 666303, China
2 Department of Biology, University of Miami, Coral Gables, FL 33124, USA
3 Graduate University of Chinese Academy of Sciences, 10049 Beijing, China
4 Agricultural Research Service, US Department of Agriculture, Reno, NV 89512, USA
5 Nevada Fisheries Resource Office, US Fish and Wildlife Service, Reno, NV 89502, USA
6 Consejo Nacional de Investigaciones Cientificas y Técnicas (CONICET) and Laboratorio de Ecologia Funcional, Departamento de Biología, Universidad Nacional de la Patagonia San Juan Bosco, 9000 Comodoro Rivadavia, Argentina
7 CONICET and Laboratorio de Ecología Funcional, Departamento de Ciencias Biológicas, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Nuñez, Buenos Aires, Argentina
8 Corresponding author (gold{at}bio.miami.edu)
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Abstract |
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Rhizophora mangle L. trees of Biscayne National Park (Florida, USA) have two distinct growth forms: tall trees (5–10 m) growing along the coast and dwarf trees (1 m or less) growing in the adjacent inland zone. Sharp decreases in salinity and thus increases in soil water potential from surface soil to about a depth of 1 m were found at the dwarf mangrove site but not at the tall mangrove site. Consistent with our prediction, hydraulic redistribution detected by reverse sap flow in shallow prop roots was observed during nighttime, early morning and late afternoon in dwarf trees, but not in tall trees. In addition, hydraulic redistribution was observed throughout the 24-h period during a low temperature spell. Dwarf trees had significantly lower sapwood-specific hydraulic conductivity, smaller stem vessel diameter, lower leaf area to sapwood area ratio (LA/SA), smaller leaf size and higher leaf mass per area. Leaves of dwarf trees had lower CO2 assimilation rate and lower stomatal conductance compared to tall trees. Leaf water potentials at midday were more negative in tall trees that are consistent with their substantially higher stomatal conductance and LA/SA. The substantially lower water transport efficiency and the more conservative water use of dwarf trees may be due to a combination of factors such as high salinity in the surface soil, particularly during dry periods, and substantial reverse sap flow in shallow roots that make upper soil layers with high salinity a competing sink of water to the transpiring leaves. There may also be a benefit for the dwarf trees in having hydraulic redistribution because the reverse flow and the release of water to upper soil layers should lead to dilution of the high salinity in the rhizosphere and thus relieve its potential harm to dwarf R. mangle trees.
Keywords: hydraulic lift, mangrove, sap flow, water relations
Received October 30, 2008; Accepted January 11, 2009