  Effects of changes in functional composition of soil communities on nutrient
cycling are still not well understood. Models simulating community dynamics
overcome the technical challenges of conducting species removal experiments in
the field. However, to date, available soil food web models do not adequately
represent the organic matter processing chain which is key for soil dynamics.
Here, we present a new model of soil food web dynamics accounting for
allometric scaling of metabolic rate, ontogeny of organic matter, and explicit
representation of nitrogen and carbon flows. We use this model to investigate
what traits are best predictors of species effects on community productivity
and on nutrient cycling. To do so, we removed 161 tropho-species (groups of
functionally identical species) one at a time from 48 forest soil food webs,
and simulated their dynamics until equilibrium. Simulations revealed that
combinations of traits better determine removal effects than single ones. The
smallest species are the most competitive ones, but carnivores of various body
masses presenting the highest connectivity and resource similarity could be key
stone species in the regulation of competitive forces. Despite this, most
removals had low effects, suggesting functional redundancy provides a high
resistance of soil food webs to single tropho-species extinction. We also
highlight for the first time that food web structure and soil fertility can
drastically change species effects in an unpredictable way. Moreover, the
exclusion of detritus and stoichiometric constraints in past studies lead to
underestimations of indirect effects and retroactions. While additional work is
needed to incorporate complementarity between detritivores, it is essential to
take into account these mechanisms in models in order to improve the
understanding of soil food web functioning.
