Plant litter decomposition is a key process in carbon and nutrient cycling. The critical role of soil‐faunal community composition in decomposition has been demonstrated using different mesh size litterbags to control exposure of litter to different faunal size classes. However, the faunal community surrounding the litterbags has not been manipulated despite potentially large indirect effects of their activity on biotic and abiotic processes that control litter decomposition at the habitat‐scale. 
We combined microcosm and litterbag techniques to facilitate a more comprehensive understanding of the role of direct and indirect effects of soil‐faunal community composition on litter decomposition. We placed litterbags of three mesh sizes across model grassland miniecosystems manipulated to enable communities containing 1) microfauna; 2) micro‐ and meso‐fauna; 3) micro‐, meso‐ and macro‐fauna. All communities contained bacteria and fungi. The approach permitted correction of mesh size artefacts inherent to field studies. Indirect effects have been divided into two separate terms, direct‐indirect effects and indirect effects. 
Decomposition in micromesh litterbags was significantly decreased by the indirect effects of meso‐ and macro‐fauna. In macrofauna communities, increased mesh size significantly increased decomposition through mesh size per se and faunal effects. Relative effects of manipulated faunal community composition on litter mass loss and C:N ratio were equivalent for green and senesced litter. The presence of meso‐ and macro‐fauna increased litter decomposition rate overall despite inhibiting decomposition by microfauna, bacteria and fungi through indirect effects.

Human impacts, including global change, may alter the composition of soil faunal communities, but consequences for ecosystem functioning are poorly understood. We constructed model grassland systems in the Ecotron controlled environment facility and manipulated soil community composition through assemblages of different animal body sizes. Plant community composition, microbial and root biomass, decomposition rate, and mycorrhizal colonization were all markedly affected. However, two key ecosystem processes, aboveground net primary productivity and net ecosystem productivity, were surprisingly resistant to these changes. We hypothesize that positive and negative faunal-mediated effects in soil communities cancel each other out, causing no net ecosystem effects.

Elevated nitrogen (N) inputs into terrestrial ecosystems are causing major changes to the composition and functioning of ecosystems. Understanding these changes is challenging because there are complex interactions between 'direct' effects of N on plant physiology and soil biogeochemistry, and 'indirect' effects caused by changes in plant species composition. By planting high N and low N plant community compositions into high and low N deposition model terrestrial ecosystems we experimentally decoupled direct and indirect effects and quantified their contribution to changes in carbon, N and water cycling. Our results show that direct effects on plant growth dominate ecosystem response to N deposition, although long-term carbon storage is reduced under high N plant-species composition. These findings suggest that direct effects of N deposition on ecosystem function could be relatively strong in comparison with the indirect effects of plant community change.

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