Microbes crucially affect on growth and survival of plant species, shaping the community structure. In this study, we estimated relative importance of symbiotic-microbes (e.g., arbuscular mycorrhizal fungi: AMF; ecto-mycorrhizal fungi: ECMF) and antagonistic-microbes (e.g.,pathogenic fungi) on plant performance for two hardwood species, Quercus serrata, and Acer mono by sowing the seeds in both forest understories and gaps. In forest understories, seeds and seedlings mortality was higher beneath conspecific- compared to heterospecific-adults in A. mono, due to severe attack of pathogenic fungi. In gaps, seedling growth and survival were usually greater in the forests dominated by conspecific- compared to heterospecific-adults in both the species, because of the higher percentage of root colonization by AM-and ECM fungi for Q. serrata and A. mono seedlings, respectively. The results suggest that relative importance of pathogenic- and mycorrhizal- fungi change according to light conditions (gaps vs. understory). Influence of mycorrhizal-fungi may also change according to presence or absence of conspecifics.