Gas exchange responses of a mangrove species, Avicennia marina, to waterlogged and drained conditions

This study was undertaken in summer on fully expanded leaves of Avicennia marina trees in the Beachwood Mangroves Nature Reserve, Durban, South Africa. Data sets were obtained over 5-7 days of relatively dry conditions and over two periods of 5 days during which the swamp was continuously inundated with dilute seawater (<150 mol m(-3) NaCl). Gas exchange responses were strongly influenced by photosynthetic photon flux density (PPFD), leaf temperature and leaf to air vapour pressure deficit law). Carbon dioxide exchange was saturated at a PPFD of about 800 mu mol m(-2) s(-1). Maximal CO2 exchange rates ranged from 8.5 to 9.9 mu mol m(-2) s(-1) with no differences between drained and waterlogged conditions. Under drained conditions, leaf conductance, transpiration and internal CO2 concentrations were generally lower, and water use efficiencies higher, than during waterlogging. Continuous waterlogging for 5 days had no adverse effect on CO2 exchange. Xylem water potentials ranged from -1.32 to -3.53 MPa during drained and from -1.02 to -2.65 MPa during waterlogged conditions. These results are discussed in relation to anatomical and metabolic adaptations of A. marina to waterlogging stress.