Blueberry is a shallow root plant in which the absorption of nutrients is inefficient, resulting in slow growth under artificial cultivation conditions. Endophytes play an important role in promoting plant growth; however, the effects of Trichoderma spp. and dark septate endophytes (DSEs) on host plant growth and soil microorganisms are still debatable. We isolated two endophytic fungal species, Trichoderma koningiopsis (TK) and a DSE (Amesia nigricolor AN), from blueberry roots, which can solubilize insoluble phosphorus and produce amylase and cellulase to promote plant growth. We found that under dual inoculation, the colonization rate and colonization intensity of TK were higher than they were under single inoculation with TK, while the colonization rate and colonization intensity of AN were lower under dual inoculation than under single inoculation with AN. The plant nutrients, root activity, available potassium, and parts of soil phosphatase activities were highest under dual inoculation. TK inoculation resulted in the highest diversity and richness in the soil fungi and bacteria, followed by dual inoculation. The abundance of Ascomycota, Acidobacteriae, Firmicutes, and Actinobacteriota increased significantly, resulting in Trichoderma and Vicinamibacteria inoculated with TK, Chaetomium and Alicyclobacillales inoculated with AN, and Hypocreales and Burkholderiaceae with dual inoculation enriched in the soil.

Dark septate endophytes (DSEs) and Phosphate-solubilizing fungi (PSFs) are widely distributed and have important application value in improving plant growth. However, the effects of DSE fungi with phosphate-solubilizing ability on host plants need further study. In this study, phosphorus-dissolving DSE fungi were screened for growth-promoting effects. We isolated, identified and characterized three DSE fungal species (Thozetella neonivea, Pezicula ericae and Hyaloscyphaceae sp.) showing phosphate-solubilizing ability. The impact of three single or dual inoculations of DSEs on blueberry plant characteristics was studied. Their effects on colonization intensity, biomass in seedlings, nutrients in plants and soil, and activities of plant resistance enzymes and soil enzymes were remarkably upregulated relative to the control (p < 0.05). The available phosphorus and acid phosphatase in different combinations were significantly increased. These findings indicate that the application of three DSEs may be valuable to facilitate the cultivation of blueberry with a higher biomass and improved plant quality.