Abstract
<title>Abstract</title> <p>Purpose Biochar can mitigate soil antibiotic resistance genes (ARGs), but the magnitude of its efficacy varies greatly, and quantitative optimization principles are lacking. This meta-analysis aims to quantify the overall effect of biochar on ARGs and identify key thresholds for its application. Methods We conducted a global meta-analysis to assess the effects of biochar on ARGs conferring resistance to sulfonamides, tetracyclines, chloramphenicols, and macrolides. Subgroup analyses were performed to evaluate the influence of biochar properties, soil conditions, application regimes, and plant co-application. Results Biochar significantly reduced target ARG abundance by 78.2% on average. The optimal application dosage was 0.5%, with a strong inhibitory window between 0.5% and 6%, beyond which efficacy declined. The effect was most pronounced in near-neutral soils (pH 6–8), but weakened under high soil nutrients (TOC > 20 g kg⁻¹, TP > 1.5 g kg⁻¹, TN > 2.0 g kg⁻¹), long-term application (> 12 months), and excessive dosage (> 10 wt%). Animal manure-derived biochar pyrolyzed at 500°C exhibited the strongest effect. Plant co-application synergistically enhanced mitigation in a species-dependent manner. Conclusion This study establishes quantitative thresholds for biochar application and demonstrates that its efficacy is modulated by soil pH, nutrient status, and application regime. These findings provide evidence-based guidance for designing context-specific biochar strategies to control soil antibiotic resistance.</p>