To investigate the effects of biochar combined with nitrogen fertilizer on vegetation， soil physicochemical properties， and extracellular enzyme activities in artificially restored bare-land grasslands in the Qilian Mountains， a randomized block design was conducted in 2021. The treatments included a basal fertilizer （biochar 0.5 t·hm^-2 + organic fertilizer 1.5 t·hm^-2） with nitrogen additions of 50， 100， 150， and 200 kg·hm^-2 （CN₁， CN₂， CN₃， CN₄）， as well as CN₀ （basal fertilizer only）， CN₅ （200 kg·hm^-2 nitrogen without basal fertilizer）， and CK （no fertilization）， totaling seven treatments. The results showed that biochar-nitrogen application significantly increased aboveground biomass （AB）， belowground biomass （BB）， and root/shoot ratio （R/S） （P<0.05）. Specifically， CN₃ significantly enhanced soil water content （SWC）， total nitrogen （TN）， soil organic carbon （SOC）， and nitrate nitrogen （NO₃^--N）， while CN₃ and CN₄ significantly promoted the activities of β-1，4-acetylglucosaminidase （NAG）， leucine aminopeptidase （LAP）， and cellobiose hydrolase （CBH） （P<0.05）. Piecewise structural equation modeling （SEM） indicated that biochar-nitrogen application improved vegetation performance and soil fertility by stimulating extracellular enzyme activities and nutrient supply. In conclusion， CN₃ （basal fertilizer + 150 kg·hm^-2 nitrogen， C∶N≈12∶1） showed the optimal effect， providing a theoretical reference for the restoration of bare-land artificial grassland in alpine regions.

Biochar and nitrogen fertilizer  /  Bare-land artificial restoration grassland  /  Soil physicochemical properties  /  Vegetation biomass  /  Extracellular enzyme activity