Plant species control and soil faunal involvement in the processes of above- and below-ground litter decomposition

Among the factors determining litter decomposition rates, the role of soil fauna as decomposers still remains unclear, especially for how they are involved in decomposing below-ground root litter compared to their relatively-known contributions to decomposing above-ground leaf litter. We conducted a litterbag experiment using two sizes of meshes and pursued the leaf and root decomposition of six major tree species in a Japanese temperate forest over 411-days to test the interactive effects of soil mesofauna and litter quality addressed based on two features (litter types and species) on the process. Moreover, given a possible correlation between litter traits of the leaves and roots, we examined whether soil mesofauna alters the relationship between leaf and root decomposition across species. We found that the effects of plant species identity was stronger than that of soil mesofauna for determining the litter mass loss rate and the microbial respiration rate in both above-ground and below-ground decomposition. In addition, we found a significant positive correlation between leaf and root litter decomposition processes, regardless of the involvement soil mesofauna. On the other hand, the presence of soil mesofauna increased microbial respiration rates in the early stage of leaf decomposition; however, soil mesofauna did not affect root microbial respiration rates during the experiment. Such differential involvement of mesofauna in the leaf and root litter decomposition may drive the general patterns of faster and slower decomposition of plant leaves and roots in the soil, respectively.