Structural changes and associated microbial activity accompanying decomposition of mangrove leaves in Mgeni Estuary

Leaves of Avicennia marina (Forssk.) Vierh. and Bruguiera gymnorrhiza (L.) Lam. were placed in litter bags and allowed to decompose in situ before collection at 7, 14, 21, 42, 64 and 85days. Material from each collection was examined for structural changes using light microscopy and SEM. Samples of each collection were also cultured for fungi and bacteria. Examination of senescent leaves still attached to the trees revealed the presence of phylloplane micro-organisms. Decomposition in both species followed a similar pattern although the leaves of A. marina decomposed more rapidly than those of B. gymnorrhiza. By day 7 there were no obvious changes in leaf structure, initial decomposition of the leaf base was the only apparent change in structure on day 14; by day 21 portions of the cuticular layer had separated from the leaf tissue; on day 42 most of the leaves were split longitudinally, separating the adaxial and abaxial surfaces; in the day-63 material, fragmentation of the leaves was evident; further fragmentation and ‘skeletonization’ of leaves was observed after 85days of decomposition. Both bacteria and fungi were important in the decomposition process. Leaves of both mangroves were found to harbour 20–25 species of fungi. This work appeared to confirm the significance of micro-organisms in the estuarine food web