Mechanical fragmentation enhances the contribution of Collembola to leaf litter decomposition

Soil fauna influence the decomposition and nutrient mineralization of leaf litter; however, the specific contributions of mechanical fragmentation (macrofauna activity) and meso-fauna to nutrient mineralization, and their interactions with litter quality, require further study. Our aim was to investigate the independent and interactive effects of litter quality, mechanical fragmentation, and Collembola density on the litter decomposition process. Intact and fragmented leaf litter from two tree species with contrasting leaf litter quality were incubated in laboratory microcosms with high and low Collembola densities. Mass loss, C, and N concentrations of the leaf litter were measured. The results showed that fragmented, low C:N ratio litter with high Collembola density had the fastest rates of decomposition and C, N mineralization, while the lowest decay rates were measured in high C:N ratio litter with low Collembola density, regardless of fragmentation. Mechanical fragmentation alone could not significantly enhance the litter decomposition in either litter type without the presence of Collembola. Meanwhile, high Collembola density without mechanical fragmentation did not significantly achieve faster litter decomposition. However, mechanical fragmentation had a positive effect on increasing N concentrations and supplied with litter of higher C:N ratio. Presence of Collembola enhanced mass loss and C, N mineralization in decomposing litter of either type significantly associated with fragmentation. The positive interaction between mechanical fragmentation and Collembola reported here emphasizes the importance of multiple trophic interactions for regulating decomposition processes, including that of physical and biological interactions among all functional groups.

► Mechanical fragmentation by macrofauna regulating net N loss during decomposition.
► Collembola contribute more to decomposition associated with fragmentation.
► Interaction of fragmentation and Collembola promoted mass loss and C, N mineralization.
► Multiple soil fauna can shape effects of litter quality on the decomposition process.