At a sedimentary site in an old mine site,Miscanthus sinensisformed patches, wherePinus densifloraseedlings could grow better compared with those outside the patches, indicating thatM.sinensiswould improveP.densifloraseedling establishment. The purpose of this study was to understand the mechanisms by whichM.sinensisfacilitates the survival ofP.densifloraseedlings by considering the soil properties, heavy metal tolerance, and root endophytes inP.densifloraseedlings at the sedimentary site. The sedimentary site, which is a bare ground, contained high concentrations of Fe, indicating that plants should be exposed to Fe and high soil temperature stresses. Measurement of soil temperature revealed thatM.sinensissuppressed sharp increases and alternation of soil temperature, resulting in reducing high soil temperature stress inP.densifloraseedlings. To adapt to the Fe stress environment,P.densifloraoutside and inside the patches produced Fe detoxicants, including catechin, condensed tannin, and malic acid.Ceratobasidium bicorneandAquapteridospora sp. were commonly isolated fromP.densifloraseedlings outside and inside the patches as root endophytes, which might enhance Fe tolerance in the seedlings.Aquapteridosporasp., which is considered as a dark-septate endophyte (DSE), was also isolated from the roots ofM.sinensis, suggesting thatM.sinensismight play a source of a root endophyte toP.densifloraseedlings.Ceratobasidium bicornecould be classified into root endophytes showing symbiosis and weak pathogenicity to host plants. Therefore, high soil temperature stress would weakenP.densifloraseedlings, causing root endophyticC.bicorneto appear pathogenic. We suggested thatP.densifloracould adapt to the Fe stress environment via producing Fe detoxicants, andM.sinensiswould facilitate the establishment ofP.densifloraseedlings in the sedimentary site by providing a DSE,Aquapteridosporasp., and maintaining symbiosis ofC.bicornefrom high soil temperature stress.