Early responses of Avicennia marina (Forsk.) Vierh. to intertidal elevation and light level

Combined effects of intertidal elevation and light level on two-month-old seedlings of Avicennia marina were studied at Zengying, Xiamen of China. Leaf number, area and thickness were promoted by decreasing elevation or elevating light level. Stem height differed little between light levels but was significantly stimulated by moderate waterlogging. Expansion of stem basal diameter was promoted by high light level but not affected by elevation. Total biomass showed highest at the middle elevation and was promoted by high light level. Seedlings in the gaps generally had higher root weight ratio (RWR) and stem weight ratio (SWR) but lower leaf weight ratio (LWR) than those under the canopy. Leaf pigment contents in the gaps were significantly stimulated by low elevations, while a reverse tendency occurred under the canopy. Both roots and leaves increased superoxide dismutase (SOD) and peroxidase (POD) activities to defend prolonged waterlogging. High light level resulted in high SOD and POD activities in roots but not in leaves. Malonaldehyde (MDA) contents changed little between light levels but were significantly promoted by prolonged waterlogging. These growth and physiological responses suggested that A. marina seedlings had strong tolerance to prolonged waterlogging but not to canopy shade. (C) 2013 Elsevier B.V. All rights reserved.