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

Abstract

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 85 days. 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 85 days 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. Blare van Avicennia marina (Forssk.) Vierh. en Bruguiera gymnorrhiza (L.) Lam. is in plantafvalsakke geplaas en toegelaat om in situ te vergaan voordat dit na 7, 14, 21, 42, 64 en 85 dae herwin is. Materiaal van elke versameling is vir strukturele veranderinge met behulp van ’n ligmikroskoop en die aftaselelektronmikroskoop ondersoek. Monsters van elke versameling is ook blootgestel aan die groei van fungi en bakterieë. ’n Ondersoek van verouderde blare wat nog aan die plante aanwesig is, het die aanwesigheid van blaargedraagde mikro-organismes getoon. Afbraak by beide spesies volg ’n soortgelyke patroon, alhoewel die blare van A. marina vinniger verrot as dié van B. gymnorrhiza. Op dag 7 was daar geen sigbare veranderinge in blaarstruktuur nie, aanvanklike afbraak van die blaarbasis was die enigste duidelike verandering in struktuur op dag 14; teen dag 21 het gedeeltes van die kutikula begin los raak van die res van die blaarweefsel; op dag 42 het die meeste blare oorlangs in ad- en abaksiale helftes verdeel; in die dag-63-materiaal is fragmentasie van die blare sigbaar; verdere fragmentasie en ‘skeletvorming’ van blare is na 85 dae van verrotting waargeneem. Bakterieë sowel as fungi het ’n belangrike rol in die afbraakproses gespeel. Blare van beide mangliete huisves tussen 20 en 25 fungi as spesies. Hierdie werk bevestig die belangrikheid van mikro-organismes in die voedselweb in strandmere.