Fungal-augmented biofertilizer increases soil nutrient availability, alters rhizosphere community structure, and improves plant growth.

Converting lignocellulosic waste into biofertilizers offers a sustainable practice for waste valorization, yet the mechanistic links underpinning how such amendments affect the soil-plant system remain poorly elucidated. We hypothesized that fungal-augmented biofertilizers improve plant growth through direct nutrient release and shifts in rhizosphere microbial community composition. To test this hypothesis, we isolated a white-rot fungus, Bjerkandera adusta strain QX3-19, which exhibited high ligninolytic activity. Inoculation with QX3-19 during composting of forest residues substantially enhanced lignocellulose degradation and yielded a nutrient-rich biofertilizer (BBF; QX3-19-augmented biofertilizer). Soil amendment with BBF significantly promoted the growth of Capsicum annuum and Cunninghamia lanceolata. Integrated metagenomic and culture-based analyses showed that BBF shifted the rhizosphere microbiome, increasing community diversity and network complexity. Specifically, BBF application was associated with the enrichment of plant growth-promoting rhizobacteria (PGPR) with complementary functional traits, alongside higher abundances of functional genes potentially involved in bacterial chemotaxis, flagellar assembly, and nutrient mineralization. Furthermore, a synthetic microbial community (SynCom) constructed from these enriched PGPR recapitulated the plant growth-promoting phenotype, suggesting a potential association between these taxa and improved plant performance. Collectively, our results suggest that QX3-19-mediated composting yields an effective biofertilizer that benefits plant growth via direct nutrient supplementation and indirect rhizosphere microbiome modulation. This integrated investigation provides empirical insights into forest residue valorization to support agroforestry sustainability.