Diurnal gas exchange characteristics and water use efficiency of three salt-secreting mangroves at low and high salinities

• Main Authors: NAIDOO, G, VON WILLERT, D. J
• Format: Conference Proceeding
• Language: English
• Subjects: Aegialitis annulata; Aegiceras corniculatum; Animal and plant ecology; Animal, plant and microbial ecology; Autoecology; Avicennia germinans; Biological and medical sciences; Brackish; Fundamental and applied biological sciences. Psychology; Marine; Plants and fungi
• ISSN: 0018-8158; 1573-5117
• DOI: 10.1007/BF00029106

Continuous measurements of gas exchange characteristics were made on two to nine year old hydroponically grown Avicennia germinans (L.) Stearn, Aegialitis annulata R. Br. and Aegiceras corniculatum (L.) Blanco maintained at 50 or 500 mol m super(-3) NaCl. In A. germinans and A. annulata, CO sub(2) assimilation rates were initially higher at 500 mol m super(-3) NaCl and decreased gradually towards the end of the photoperiod when rates were similar to those at the lower salinity. In A. corniculatum, assimilation rates were higher at 50 mol m super(-3) NaCl and about 55% lower at the higher salinity. In all three species, leaf conductance and transpiration exhibited trends similar to those for CO sub(2) assimilation. Intercellular CO sub(2) concentrations were similar at both salinities in A. germinans and A. annulata, but considerably higher at the lower salinity in A. corniculatum. Water use efficiencies (WUE), although similar between salinity treatments in A. germinans and A. annulata, were greater at the higher salinity in A. corniculatum . Data obtained from CO sub(2) response curves indicated that assimilation at high salinity in A. corniculatum was limited by conductance, and to a lesser extent, by photosynthetic capacity. In A. germinans and A. annulata, assimilation was greater at the higher salinity as indicated by increase in both the initial slope and the upper plateau of the CO sub(2) response data. Greater assimilation at high salinity in A. germinans and A. annulata may be attributed to lower carbon losses via photorespiration and to efficient salt excretion and sequestration.