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Abstract: Increases in atmospheric nitrogen (N) deposition are known to alter the ground vegetation of forest ecosystems by promoting nitrophilic plant species and displacing nitrogen-sensitive, oligotrophic species. Though there are well-known indicator species for eutrophication, there is often no direct verifiable relationship between N deposition and the strength of the eutrophication signal in the vegetation. The key reason for this sometimes lacking or weak relationship is that significant amounts of plant-available reactive N (Nr) are provided from the decay and mineralization of organic matter in the course of N cycling within the forest. The relationship is further complicated as N mineralization is also influenced by external N inputs. It has been shown repeatedly that various soil parameters related to acidity can confound a close N deposition-vegetation relationship, because acidity exerts a strong influence on the decomposition of organic matter. To further improve the understanding of the complex relationships between soil variables and vegetation composition, we analyzed vegetation and soil chemistry in acidophilous broad-leaved temperate forests of southwestern Germany, dominated by beech and oak. Our results suggest that manganese (Mn) availability likely is another factor modifying the eutrophication signal of the ground vegetation. In our analyses, the eutrophication signal in the vegetation was strongly related to high exchangeable Mn concentrations from the soil matrix and high Mn concentrations in the soil solution, in some cases to a greater extent than to parameters that reflect soil acidity. This response may be attributed to the function of Mn as a cofactor in the Mn peroxidase of white-rot fungi, which are the initiators of the decomposition of lignified organic matter. Since Mn depletion following previous acidic deposition is common in Central European forests, such a disconnection of the eutrophication signal in the vegetation from atmospheric N deposition might be widespread in forests on acidic soils