The mechanisms and effects of interaction among the factors that control decomposition and mineralization in terrestrial systems are still not fully understood. This is especially true for the interactions between the quality of resources and the structure of the soil community. In this paper we explore one potential way in which the composition of the soil community could affect nitrogen mineralization from litter: by mediating the control that the quality of litter exerts on the structure of the micro-food web. In a factorial arrangement, we exposed soil to six types of surface-applied litter of contrasting chemical compositions and restricted the access of size classes of fauna to mineral soil. During six months of decomposition we assessed the effects of litter type on the structure of  the microbial community, nematodes and microarthropods in the mineral soil when fauna had been excluded and when it was present, and measured nitrogen mineralization and under both scenarios after 21, 91 and 165 days. We expected that if an effect of fauna on the strength of the control of nitrogen mineralization by litter quality was detected, it would be associated with corresponding changes in the microbial community and its direct consumers.

Results/Conclusions

The composition of soil fauna affected the strength of the control of nitrogen mineralization by the chemical quality of plant litter. Specifically, we found that the influence of the chemical composition of litter (C/N, %N, %P, %C) was enhanced when the larger members of the soil fauna were not excluded from the system. Our results suggested that the presence of fauna affected nitrogen mineralization by affecting the abundance of the consumer level of the micro-food web, the nematodes in particular. Our study also indicated that that the presence of larger fauna accentuated the response of the microbial community to the quality of litter and therefore supported the hypothesis that the effect of litter quality on mineralization can be mediated by the effect of fauna on the micro-food web.