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 the course of the interdisciplinary program, "Ecosystem Research in the Bornhoved Lake District." The microbiological data were combined to evaluate the functional status of the Histosols. It was hypothesized that carbon accumulation 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 the forest. Rates of leaf litter decomposition, in situ soil C mineralization, and in situ N-2-fixation were higher at the wet site. Furthermore, the composition of the bacterial communities and the presence of ectomycorrhizas indicated sufficient O-2 availability and high microbial vitality in the soil at the wet site. An anthropogenic lowering of the lake water table during the 1930s seems still to control the actual soil conditions, resulting in humus degradation in the two Histosols of the forest. The two soils clearly 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 supply nutrients, although humus decay may possible be decelerated by a temporarily high water table and refractory humic substances.