Hydraulic redistribution in dwarf Rhizosphra mangle trees driven by interstitial soil water salinity gradients: impacts of hydraulic architecture and gas exchange

GUANG-YOU HAO, TIM J. JONES, CORENE LUTON, YONG-JIANG ZHANG, ERIC MAZANE, FABIAN G. SCHOLZ, SANDRA J. BUCCI, KUN-FANG CAO AND GUILLERMO GOLDSTEIN

TREE PHYSIOLOGY

Heron Publishing

Año: 2009 vol. 29 p. 697 - 705

0829-318X

 Rhizophora mangle L. trees of Biscayne National Park (Florida, USA) have two distinct growth forms: tall trees (5 to 10 m) growing along the coast and dwarf trees (1 m or less) in the adjacent inland zone. Sharp decreases in salinity and thus increases in soil water potential from surface soil to about 1 m deep were found at the dwarf mangrove 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 the nighttime, early morning and late afternoon in dwarf trees, but not in tall trees. In addition, hydraulic redistribution was observed throughout 24 hour periods during a low temperature spell. Dwarf trees have 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 have lower CO2 assimilation rate and lower stomatal conductance compared to tall trees. Leaf water potentials at midday were more negative in tall trees consistent with their substantially higher stomatal conductance and LA/SA. The substantially lower water transport efficiency, and 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. We suggest that there may also be a benefit for the dwarf trees in having hydraulic redistribution because 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 the potential harm to dwarf R. mangle trees.