Biology and Physiology of Avicennia Marina in the Coastal Conditions of Southern Morocco

Abstract

To introduce Avicennia marina in some bays of Morocco, a planting test has been carried out in the bay of Agadir. The plantation failed mainly due to human pressure and natural stress (wind); however, these effects could have been reduced through taking necessary measures during the first stages of plantation. As a follow-up to this failure, and to better understand the optimum conditions for the establishment of A. marina under Moroccan conditions, several experiments are carried out; one of these was the vegetative propagation of the species and growth under different salinity levels. It is observed that air layering showed encouraging results, when 30% of plants produced thick roots after 5 months. The performance of 6-month-old Avicennia marina plants was evaluated in quick check system (QCS) using five water salinity levels (0, 50, 75, 100 and 150% seawater) and by studying limit of salt tolerance, growth and some physiological parameters. The number of leaves, length and area, stem diameter, branching and biomass showed a similar trend, that is, maximum values were obtained in 50% seawater. The threshold of salt tolerance exceeded 150%. Ions concentration (K⁺, Na⁺, Ca²⁺ and Mg²⁺), relative water content (RWC), protein content and osmotic potential of different parts of the plants showed that Avicennia marina adapts physiologically to survive under very high salt stress conditions. Ions concentration increased with increasing salinity (0.59 g/100 g and 2.35 g/100 g of Na⁺ at 0 and 150% seawater, respectively, in leaves), and their content in the shoots was higher than in the roots. In consequence, osmotic potential was lower in plants grown in high salinity (−12.24 bars at 0% and −37.45 bars at 150% seawater in roots).