Decomposition of dead plant material and soil organic matter (SOM) is a key ecosystem process mediated by soil microbial communities. Structure, function and activity of these communities, is in turn partly regulated by SOM quality and nutrient availability, which can exhibit great variation in response to plant species, season, site characteristics, and anthropogenic influences such as nitrogen inputs. An understanding of how variations in substrate quality and nutrient availability shape structure and function of microbial saprotrophic communities is
pivotal to better understand ecosystem services such as C-sequestration under global change. Here, we summarize results from three metaproteomic experiments aimed at linking structure and function of microbial decomposing
communities to nutrient availability and/or C-sequestration across metaproteomic experiments. Among them are (i) identifying microbial communities active during the decomposition of beech leaf litter from different sites with varying nutrient contents (ii) linking microbial community structure and functions to coniferous forest-floor decomposing processes (iii) measuring the effects of long term forest N-addition on decomposer communities and C-storage in a temperate podzol. Fungi play a central role as producers of degrading enzymes while bacteria seem to benefit from the presence of fungal enzymes during litter degradation. Cellulase production was observed as an important factor for decomposition. Bacterial phyla that developed on forest floor of different tree species were driven by the N content of their substrate, while fungal phyla seemed to be related to the C-content. Chronic nitrogen additions decreased the relative abundance of ascomycotal proteins and increased the abundance of plant proteins in the Oe horizon of a 100y old spruce forest. At the same time, organic horizon C storage increased by 30% consistent with the idea that N suppresses fungal decomposers.
