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The classical view that aboveground litter is the main resource for the soil food web is challenged by recent studies, indicating the importance of belowground resources, such as root exudates to be underestimated. Our study aimed at disentangling the relative importance of root-derived resources for soil food webs and to quantify the relative contribution of aboveground litter and root-derived substances for soil microorganisms. Further, the study aimed at evaluating the role of identity and diversity of root and litter species for soil microorganisms. Therefore, two year old tree saplings of four deciduous tree species (Fagus sylvatica, Acer pseudoplatanus, Fraxinus excelsior, Tilia cordata) differing in the associated mycorrhizal fungi (EMF or AMF) and litter quality (high and low), were planted in a 150 year old mountain oak forest (Quercus petraea). For the first time aboveground litter and root species were manipulated independently. The response of soil microorganisms to variations in resources was measured by substrate-induced respiration (SIR) and phospholipid fatty acid (PLFA) analysis. Soil microorganisms generally did not respond to the presence of roots, type of mycorrhizal fungi or root identity and diversity. In contrast, aboveground litter affected basal respiration and community composition of soil microorganisms, suggesting litter to be of higher importance for the soil food web as compared to root-derived resources, at least in consideration of young trees. Unexpectedly, there was no beneficial leaf litter mixture effect; rather, microbial community significantly varied with litter quality and identity, with contrasting effects on different soil microorganisms. Overall, the results point to a stand age dependent importance of aboveground and belowground resources for decomposer food webs of forest ecosystems, with effects of litter quality and identity on mineralization processes and feedbacks to plants being most significant for young trees, i.e. during stand regeneration.