Effects of salinity and vapour pressure on gas exchange and water use in mangroves from northern Australia and Papua New Guinea

Gas exchange measurements were made on exposed sun leaves from 19 mangrove species (10 genera and 8 families) from 9 estuaries in north eastern Australia and Papua New Guinea. The estuaries varied in salinity and climatic regimes.The Australian localities included 5 sites in Queensland (Norman River, Daintree River, Trinity Inlet, Murray River, and Missionary Bay (Hinchinbrook Island) and one site in the Northern Territory (McArthur River). In Papua New Guinea the sites were Era, Wapo and Ivi Rivers (Gulf of Papua), Galley Reach and Motupore Island.Gas exchange measurements were made on between 2 and 27 leaves from each species sampled at each site. Leaves exposed to irradiances above 800 µmol/m²/s were chosen. Measurements were made with a portable photosynthesis system with a purpose designed leaf cuvette. Measurements were made of leaf temperature, the relative humidity and air temperature inside the cuvette. Gases were analysed with an infrared gas analyser. Barometric pressure was measured daily with an aneroid barometer. Ambient relative humidity was measured with an aspirated wet and dry bulb thermometer at 9am and 3pm.The data collected were used to calculate CO2 assimilation rate, stomatal conductance to CO2, intercellular CO2 concentrations and intrinsic water use efficiency. Soil salinity was measured in samples of the pore water, which drained into a 0.45 core hole. Samples were taken at a number of locations within each site. This field study was undertaken to determine whether salinity and leaf to air vapour pressure deficit influence photosynthetic carbon fixation and water use efficiency in mangroves.

本研究针对澳大利亚东北部与巴布亚新几内亚境内9处河口的19种红树植物（隶属于10个属、8个科）的暴露型向阳叶片开展气体交换测定。这些河口的盐度与气候条件均存在差异。澳大利亚境内的采样点包括昆士兰州的5处站位（诺曼河、丹特里河、三一湾、默里河以及欣钦布鲁克岛的传教士湾），以及北领地的1处站位（麦克阿瑟河）；巴布亚新几内亚境内的采样点则包括埃拉河、瓦波河与伊维河（巴布亚湾区域）、盖利水道以及莫图普雷岛。每个站位的每个红树物种均采集2至27片叶片用于气体交换测定，实验选取的叶片均处于光照强度高于800 μmol/m²/s的环境中。测定采用便携式光合测定系统（portable photosynthesis system）搭配定制化叶室（leaf cuvette）完成，同步记录叶室内的叶片温度、相对湿度与空气温度。气体成分通过红外气体分析仪（infrared gas analyser）完成检测；每日采用无液气压计（aneroid barometer）测定大气压强，并于每日上午9时与下午3时，采用通风式干湿球温度计（aspirated wet and dry bulb thermometer）测定环境相对湿度。所采集的数据被用于计算二氧化碳同化速率、二氧化碳气孔导度、胞间二氧化碳浓度以及内在水分利用效率。土壤盐度通过孔隙水样本测定，样本取自0.45口径钻孔所渗出的孔隙水；每个站位内的多个点位均采集了此类样本。本野外研究旨在探究盐度与叶-空气水汽压亏缺是否会影响红树植物的光合碳固定过程与水分利用效率。