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PHYSIOLOGICAL ADAPTATIONS OF AVICENNIA MARINA TO SEAWATER CONCENTRATIONS IN THE INDUS DELTA, PAKISTAN

IRFAN AZIZ AND M. AJMAL KHAN

Abstract: Avicennia marina is the most dominant species among mangroves found in the lndus delta, Pakistan, alongwith a few populations of Aegiceras corniculata, Rhizophora mucronata and Ceriops tagal. Propagules of Avicennia marina collected from the lndus delta were grown in pots containing sandy soil that were subirrigated with 0, 25, 50, 75 and 100% seawater fortified with nitrogen. Growth and physiological responses recorded at seedling and sapling stages showed a maximum growth in 50% seawater which declined with an increase in salinity. All the other growth parameters followed more or less a similar pattern. Xylem pressure potential showed a strong positive relationship, while osmotic potential, water potential and stomatal conductance a strong negative relationship with the increase in media salinity. Proline concentrations substantially increased in treatments up to 50% seawater showing no change with further increase in salinity. Oxalate concentration decreased with increase in salinity. Sodium and chloride ions increased substantially while calcium, magnesium and potassium decreased with an increase in seawater concentrations.

Department of Botany, University of Karachi, Karachi-75270, Pakistan.