Tree species-mediated soil properties shape soil fauna community structure more strongly in the soil layer: Evidence from a common garden experiment

Soil fauna plays a crucial role in the soil biogeochemical cycles of forest ecosystems, with tree species composition regulating their diversity and functionality through alterations in habitat conditions and nutrient availability. However, identifying the impacts of tree species on soil faunal communities remains challenging due to the difficulty in distinguishing the effects of tree species-induced habitat changes from those of historical environmental conditions. Here, we conducted a field study in a common garden established in 2015, with consistent climate, soil, and land-use conditions to clarify the response of the soil faunal community to changes in tree species. After 5 years of plantation growth, we evaluated the differences in tree species identities and soil faunal community structures between the litter and soil layers in four closed-canopy broadleaf forests (Cinnamomum septentrionale, Cinnamomum camphora, Cinnamomum longepaniculatum and Toona sinensis). We found that the soil faunal communities differed significantly among the four broad-leaved tree species, with 18.7 % being dominated by Collembola and 67.2 % by Acari, with a relatively high proportion of microbivores (65.5 %). Compared with that of the other stands, the C. longepaniculatum stand had the most notable differences in taxa composition, while the T. sinensis stand exhibited the greatest soil biological quality, with a QBS value 1.25 times greater than that of other stands. The greatest total soil faunal abundance was observed in C. camphora, and this high abundance was due to a greater proportion of microbivores (75.4 %), whereas the detritivores, herbivores, and predators exhibited greater abundance in T. sinensis than in the other stands due to the high-quality litter input (low C/P and C/N ratios) and low tree biomass. The distribution of soil fauna across the habitat layers was significantly influenced by tree species changes, with the most pronounced differences occurring in the soil layer rather than in the litter layer. Finally, soil properties, rather than litter and plant conditions, were the primary factors explaining interspecific variations in total abundance and total diversity of the soil fauna and the QBS index, accounting for 61.6 %, 71.7 %, and 34.4 % of the variation, respectively. The results from the common garden experiment suggest that the change in the soil faunal community due to tree species identity was greater in the soil layer than in the litter layer, with the crucial determinant being tree-species-mediated soil properties. These insights enhance our understanding of the effect of tree species on soil faunal communities, which is essential for biodiversity conservation in artificial forests and for guiding tree species selection.