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.