Plant-soil feedback (PSF) is crucial in shaping plant community and ecosystem dynamics. While plant species-specific effects on soil microbial communities have been extensively studied, the impact of plant density during the conditioning of soil microbes remains largely unexplored. In classic PSF experiments, conditioning phase duration and plant density are often set arbitrarily without systematically tracking their effects on microbial communities. Here, we examine whether soil microbial community development is density-dependent, i.e., does it accelerate under high plant densities? We established an experiment using Machilus zuihoensis seedlings at two densities (1 or 4 plants per pot) in soils inoculated with either conspecific-conditioned soil (i.e., home soil collected beneath M. zuihoensis individuals) or heterospecific-conditioned soil (i.e., away soil collected beneath Engelhardia roxburghiana individuals). Unplanted pots served as controls. We characterized soil fungal communities by monthly harvesting three pots from each soil and density combination and analyzing fungal community composition through Illumina-based amplicon sequencing. We also harvested seedlings and weighed their dry biomass monthly. Principal Coordinate Analysis revealed significant differences between home and away soil treatments, indicating the persistence of species-specific microbial communities despite seedling presence. However, we found no significant difference among density treatments. These results suggest that seedling conditioning capacity might be low due to their slow ontogenetic development. Therefore, we may conclude that our experimental duration is too short to detect meaningful soil conditioning relative to the tree's life cycle. Nevertheless, this finding provides valuable insights into experimental design for PSF studies focusing on forest ecosystems.