Hydraulic redistribution in dwarf Rhizophora mangle trees driven by interstitial soil water salinity gradients: impacts on hydraulic architecture and gas exchange
Hydraulic redistribution in dwarf Rhizophora mangle trees driven by interstitial soil water salinity gradients: impacts on hydraulic architecture and gas exchange
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DOI：
10.1093/treephys/tpp005
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发表时间：
2009-05-01
期刊：
影响因子：
4
通讯作者：
Goldstein, Guillermo
中科院分区：
文献类型：
--
作者：
Hao, Guang-You;Jones, Tim J.;Goldstein, Guillermo
美国佛罗里达州比斯坎国家公园（Biscayne National Park）的Rhizophora mangle L.树木有两种不同的生长形式：沿海岸生长的高大树木（5-10米）和邻近内陆地区生长的矮树（1米或以下）。在矮红树地，土壤盐度急剧下降，从而使土壤水势从表层土壤增加到约1英寸深，而在高红树地则没有。与我们的预测一致，在夜间、清晨和下午晚些时候，矮树的浅支柱根部通过反向液流检测到的水力再分配在夜间、清晨和下午晚些时候被观察到，而在高大的树木中没有。此外，在低温期间的24小时内观察到水力再分配。矮树的叶面比水力导率显著低于矮树，叶面管直径较小，叶面积与叶面比（LA/SA）较低，叶尺寸较小，叶质量较高。矮乔木叶片CO2同化速率和气孔导度均低于高大乔木。高大乔木中午叶片水势为负，这与高大乔木较高的气孔导度和LA/SA一致。矮树的水运效率较低，水分利用较为保守，这可能是由于多种因素的综合作用，如表层土壤的高盐度，特别是在干旱时期，以及浅层根系大量的反向汁液流动，使高盐度的上层土壤成为蒸腾叶片的竞争性水汇。水力再分配对矮树也有好处，因为反向流动和向上层土壤释放水分会导致根际高盐度的稀释，从而减轻其对矮树的潜在危害。
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 I in 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 stein 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.