Fungal succession and changes in the fungal degradation potential during the initial stage of litter decomposition in a black alder forest (Alnus glutinosa (L.) Gaertn.)

The succession of fungal decomposers over the first year of litter breakdown at two sites (wet and moist) of a black alder forest in Northern Germany was investigated. The active fungi were isolated after separation from dormant propagules by a litter washing method. Their decomposition potential was determined in vitro by investigating the amylase, protease, lipase, xylanase, polygalacturonase, pectinlyase, cellulase and laccase activities. Based upon the observed frequency and enzymatic potential of the isolates, the total fungal degradation potential was determined. In the initial phase of the decomposition a zymogenic microflora of the genera Mucor, Alternaria and Epicoccum colonized the litter. This flora was progressively replaced by autochthonous species, principally of the genus Fusarium. with only few exceptions, the fungal succession was similar on the litter of both sites. The amylase potential was consistently large during the whole investigation, whereas the laccase potential remained small with no significant variations. On the contrary, all other enzymatic potentials underwent complex variations, that were related to the fungal succession. These variations were similar at both sites and were in accordance with results of similar studies. Nevertheless, the interest and importance of such variations in enzymatic potentials has to be verified by chemical analysis of litter decomposition.