Biochar Mitigates Root Exudate-Induced Priming of Native SOC Decomposition via Soil Phosphorus Availability and Microbial Structure

Biochar amendment is increasingly recognized as a promising strategy for enhancing soil carbon sequestration in cropland systems; however, the mechanisms governing its effects on root exudate-induced decomposition of native soil organic carbon (SOC) remain poorly understood. We conducted a controlled laboratory incubation experiment using 13C-labeled glucose as a proxy for root exudates to quantify native SOC decomposition in wheat soil with or without long-term biochar amendment. Glucose addition induced a strong positive priming effect in unamended control soils, increasing native SOC decomposition by 354.4 μg CO2 g−1 soil over 30 days, whereas biochar amendment substantially suppressed this response by 75.7%. This suppression was attributed to biochar-enhanced phosphorus availability and a shift in microbial community composition toward greater fungal dominance, which collectively reduced microbial nutrient mining from native SOC pools. Our findings demonstrate that biochar can effectively mitigate the priming effect through coordinated alterations in nutrient dynamics and microbial community structure, thereby promoting long-term SOC stabilization. These results strengthen the scientific basis for biochar application as a climate change mitigation strategy in agricultural ecosystems.