Growth and salt balance in two species of mangroves from north Queensland in relation to salinity

Mature propagules of two mangrove species, Avicennia marina and Rhizophora stylosa, were collected at Cape Ferguson, north Queensland in February 1981 and transferred to a shadehouse at the Australian Institute of Marine Science. The shadehouse was naturally lit and screening reduced the photon irradiance incident on the plants to about one-third of that outside the shadehouse. Air temperature inside the shadehouse was not controlled and ranged between a minimum of 17°C in winter and a maximum of 37°C in summer.Avicennia marina propagules were placed in a tray of 25% seawater for 2 days to allow the pericarp to be shed. They were then planted out into trays containing washed beach sand saturated with 25% seawater to promote root formation. Root formation by Rhizophora stylosa propagules was induced by standing the basal end of the propagule in 25% seawater.After 4 weeks, seedlings were transferred to individual 2.4 litre plastic pots containing one of 5 treatments. Salinity treatments of 0, 25, 50, 75 and 100% seawater were prepared by mixing seawater with tapwater, and a solution containing major and minor nutrients was added to each treatment. Four plants of each species were placed in each treatment. The culture solutions were initially changed monthly and later at 2 weekly intervals, as the seedlings became larger. The water level in the pots was maintained by adding tapwater containing < 1 mM sodium and chloride.In February 1982, the number of leaves remaining on each plant was counted and the number lost through senescence was obtained by counting leaf scars. Plants were then washed thoroughly with tapwater to remove surface salt, blotted with paper towelling, and subdivided into component parts, which were weighed and then dried to constant weight at 80°C. The total area of leaves remaining on the plant was measured with a Licor leaf-area meter. The dry weight and area of leaves lost through senescence was calculated from the number of leaves lost and, respectively, the mean dry weight and mean area per living leaf.The dried plant samples were ground for 30 seconds in a tungsten carbide mill. For analyses of sodium, potassium, calcium and magnesium, 1 g dry weight was pressure digested with 10 ml of concentrated HNO3 in a polycarbonate bottle for 16 h at 60°C. Extracts were analysed by the Australian Mineral Development Laboratory, Adelaide, S.A. using an inductively coupled plasma emission spectrometer calibrated using NBS leaf samples. For chloride, 100 mg of ground sample was digested at 80°C in 20% (v/v) HNO3, filtered, and the extracts analysed for chloride with a Radiometer CMT10 coulometric chloride titrator.
This study was undertaken to examine salt tolerance in Avicennia marina (which has salt secreting glands in its leaves) and Rhizophora stylosa (which does not have these glands), by monitoring growth under different salinity regimes over a period of one year. The contribution of the more common cations and anions in seawater to osmotic adjustment in both species was also examined.

1981年2月，于澳大利亚昆士兰州北部的弗格森角（Cape Ferguson）采集了两种红树植物——白骨壤（Avicennia marina）与柱果红树（Rhizophora stylosa）的成熟繁殖体，并将其转移至澳大利亚海洋科学研究所（Australian Institute of Marine Science）的荫棚内。该荫棚采用自然光照，通过遮光幕将植株接收的光子辐照度降至棚外的约1/3；荫棚未设置温度控制系统，气温波动范围为冬季最低17℃、夏季最高37℃。

将白骨壤的繁殖体置于盛有25%浓度海水的托盘内静置2天，使其果皮脱落；随后移栽至铺有经冲洗海滩砂的托盘，以25%浓度海水饱和砂质基质以促进根系萌发。柱果红树的繁殖体则通过将其基部浸入25%浓度海水中，诱导根系形成。

培养4周后，将幼苗移栽至单个2.4升塑料盆中，共设置5种盐度处理组：通过将海水与自来水混合，配制盐度分别为0%、25%、50%、75%和100%的培养液，并向每组添加含大量及微量营养元素的营养液。每个处理组各放置4株同物种的幼苗。随着幼苗生长，培养液最初每月更换一次，后续改为每两周更换一次；盆内水位通过添加含钠、氯离子浓度均低于1 mM的自来水维持。

1982年2月，统计每株植株的存活叶片数，并通过计数叶痕计算因衰老脱落的叶片数。随后用自来水彻底冲洗植株以去除表面盐分，用纸巾吸干水分，将植株拆分为各组分器官分别称重，之后置于80℃下烘干至恒重。使用LI-COR叶面积测定仪（Licor leaf-area meter）测量植株存活叶片的总叶面积。根据脱落叶片数，结合单株存活叶片的平均干重与平均叶面积，分别计算出衰老脱落叶片的总干重与总叶面积。

将烘干的植物样品置于碳化钨研磨机中研磨30秒。针对钠、钾、钙、镁元素的分析，称取1 g干样置于聚碳酸酯瓶中，加入10 mL浓硝酸，于60℃下加压消解16小时。萃取液由南澳大利亚州阿德莱德的澳大利亚矿物开发实验室采用电感耦合等离子体发射光谱仪进行分析，该仪器以美国国家标准局（NBS）标准叶片样品进行校准。针对氯离子的分析，则称取100 mg研磨后的样品，于80℃下在20%（体积比）硝酸溶液中消解后过滤，使用雷迪美特CMT10库仑法氯离子滴定仪测定萃取液中的氯离子含量。

本研究旨在通过为期一年的监测，探究两种红树植物在不同盐度条件下的生长情况，以分析白骨壤（叶片具泌盐腺体）与柱果红树（无泌盐腺体）的耐盐性；同时探讨海水中常见阴阳离子对两种植物渗透调节的贡献。