Revealing the bottom-up effects of plant community on soil fauna and microbial diversity can better understanding the biodiversity maintaining mechanisms at multi-trophic levels. Previous studies have mainly focused on the effects of plant species diversity on soil fauna and microbial diversity, but the bottom-up effects of the vegetation functional composition received less attention. In this study, we firstly analyzed the relationships among deciduous woody plant proportion, tree and herbaceous species diversity, and soil fauna and bacteria diversity across 13 plant communities on Dajinshan Island, Shanghai. Then the structure equation model was used to distinguish the direct and indirect effects of deciduous woody plant proportion on soil faunal and bacterial diversity. The results showed that the proportion of deciduous wood plants had not only direct positive and negative effects on herbaceous species diversity (P<0.01) and soil fauna diversity (P<0.05), respectively; but also indirectly decreased soil bacteria diversity through the cascading effect of herbaceous species (P<0.10). However, woody plant diversity positively only linked with herbaceous species diversity, and did not correlate with soil fauna and bacteria diversity (P>0.10). These results suggest that, compared to tree species diversity, the proportion of deciduous plants plays more important role in sustaining biodiversity patterns across multi-trophic levels in forest ecosystems in the northern margin of the middle subtropical regions.