Fig. 1

Effects of biochar amendments on microbial carbon metabolic activities (a) and soil metabolic quotient (b; qCO₂) in the flied experiment. Carbon source utilization rates based on six specific carbon families are analyzed by the Biolog EcoPlates including carbohydrates, carboxylic acids, amino acids, polymers, phenolic acid, and amines/amides (c). Microbial carbon metabolism is reflected by the average well color development (AWCD). Bars with different lowercase letters indicate statistical significant differences (P < 0.05) as revealed by Bonferroni’s post hoc tests. CK, no fertilizer; CF, conventional fertilization; LB, low biochar with 2400 kg ha⁻¹ year⁻¹; MB, medium biochar with 7200 kg ha⁻¹ year⁻¹; HB, high biochar with 12,000 kg ha⁻¹ year⁻¹