The utilization of Caragana korshinskii residues as forage is constrained by their lignified structure and limited digestibility. In this study, eleven wild Irpex lacteus isolates collected from C. korshinskii habitats in western Inner Mongolia were screened for substrate colonization and lignocellulose-degrading potential. All isolates colonized shredded C. korshinskii residue medium, while isolates n4 and n6 reached the maximum measurable colony diameter of 70.00 mm after 7 d. Guaiacol, aniline blue, and carboxymethyl cellulose-Congo red assays revealed isolate-dependent differences in oxidative and cellulolytic responses. Among four isolates selected for quantitative enzyme analysis, isolate n6 exhibited the highest laccase, lignin peroxidase, and manganese peroxidase activities, reaching 3.59, 11.33, and 9.30 U mL − 1 , respectively, together with the highest filter paper activity; its β -glucosidase activity was also among the highest measured. Orthogonal screening and validation identified maltose, peptone, initial pH of 4.5, and 30°C as suitable conditions for mycelial growth. Among the five grain substrates tested, buckwheat supported the most rapid inoculum propagation. After 56 d of solid-state fermentation, inoculation with I. lacteus n6 following pasteurization reduced the measured concentrations of neutral detergent fiber, acid detergent fiber, and acid detergent lignin by 16.78%, 16.54%, and 49.19%, respectively, relative to the corresponding uninoculated control. The measured crude protein and water-soluble carbohydrate concentrations increased from 8.18% to 12.10% and from 0.99% to 5.53%, respectively. These findings demonstrate the potential of a locally derived I. lacteus isolate for pasteurization-assisted solid-state bioconversion of C. korshinskii residues and provide a basis for their forage-oriented valorization.