Microbial processes and features of the microbiota in histosols from a black alder (Alnus glutinosa (L.) Gaertn.) forest

Microbiological features and in situ microbial activities were analyzed in soils at a black alder forest adjacent to the eutrophic Lake Belau during t he course of the interdisciplinary program, "Ecosystem Research in the Born hoved Lake District." The microbiological data were combined to evaluate th e functional status of the Histosols. It was hypothesized that carbon accum ulation typical for Histosols would mainly take place at the wet part ("wet site") close to the lake shore and not at the drier part ("dry site") of t he forest. Rates of leaf litter decomposition, in situ soil C mineralizatio n, and in situ N-2-fixation were higher at the wet site. Furthermore, the c omposition of the bacterial communities and the presence of ectomycorrhizas indicated sufficient O-2 availability and high microbial vitality in the s oil at the wet site. An anthropogenic lowering of the lake water table duri ng the 1930s seems still to control the actual soil conditions, resulting i n humus degradation in the two Histosols of the forest. The two soils clear ly differed in productivity and C and N cycling, being controlled either by upland, acid runoff or by eutrophic lake water. Lake water seems to buffer but also to intensify microbial transformations at the wet site and to sup ply nutrients, although humus decay may possible be decelerated by a tempor arily high water table and refractory humic substances.