Naidoo G
School of Biological and Conservation Sciences, University of KwaZulu-Natal, P/B X 54001, Durban, 4000, South Africa.
Ann Bot. 2006 Jun;97(6):1095-101. doi: 10.1093/aob/mcl064. Epub 2006 Mar 24.
In Richards Bay, South Africa, Avicennia marina frequently exhibits a distinct productivity gradient, with tree height decreasing markedly from 6-10 m in the fringe zone to <1.5 m in the dwarf zone which is 120 m inland at a slightly higher elevation. In this investigation, soil physico-chemical conditions between fringe and dwarf A. marina were compared and the constraints imposed by any differences on mangrove ecophysiology and productivity determined.
Soil and plant samples were analysed for inorganic ions using spectrophotometry. Gas exchange measurements were taken with an infrared gas analyser and chlorophyll fluorescence with a fluorometer. Xylem psi was determined with a pressure chamber and chlorophyll content with a chlorophyll absorbance meter.
In the dwarf site, soil salinity, total cations, electrical conductivity and soil concentrations of Na(+), K(+), Ca(2+), Mg(2+), Zn(2+), Mn(2+) and Cu(2+) were significantly higher than those in the fringe zone. Soil water potential and the concentration of soil P, however, were significantly lower in the dwarf site. In the leaves, Na(+) was the predominant ion and its concentration was 24 % higher in dwarf than fringe mangroves. Leaf concentrations of K(+), Ca(2+), Mg(2+), Mn(2+) and P, however, were significantly lower in dwarf mangroves. Photosynthetic performance, measured by gas exchange and chlorophyll fluorescence, was significantly reduced in the dwarf plants.
The results suggest that hydro-edaphic factors contribute to high soil salinities, low water potentials, water stress and ion imbalance within tissues including P deficiency, which in interaction, contribute to dwarfing in Avicennia marina.
在南非的理查兹湾，白骨壤常常呈现出明显的生产力梯度，树高从边缘地带的6 - 10米显著降低至矮化地带（位于内陆120米、海拔略高之处）的不足1.5米。在本研究中，对边缘地带和矮化地带的白骨壤之间的土壤理化条件进行了比较，并确定了这些差异对红树林生态生理学和生产力所造成的限制。
使用分光光度法分析土壤和植物样本中的无机离子。用红外气体分析仪进行气体交换测量，并用荧光计测量叶绿素荧光。用压力室测定木质部水势，用叶绿素吸光计测定叶绿素含量。
在矮化地带，土壤盐分、总阳离子、电导率以及土壤中钠（Na⁺）、钾（K⁺）、钙（Ca²⁺）、镁（Mg²⁺）、锌（Zn²⁺）、锰（Mn²⁺）和铜（Cu²⁺）的浓度显著高于边缘地带。然而，矮化地带的土壤水势和土壤磷浓度显著较低。在叶片中，钠（Na⁺）是主要离子，其在矮化红树林中的浓度比边缘红树林高24%。然而，矮化红树林中钾（K⁺）、钙（Ca²⁺）、镁（Mg²⁺）、锰（Mn²⁺）和磷的叶片浓度显著较低。通过气体交换和叶绿素荧光测量的光合性能在矮化植株中显著降低。
结果表明，水文土壤因素导致土壤高盐度、低水势、水分胁迫以及组织内离子失衡（包括磷缺乏），这些因素相互作用导致白骨壤矮化。
