Microbial biomass carbon (MBC) under different treatments (CK: control, B4.5: 4.5 t ha⁻¹ yr⁻¹ biochar addition, B9.0: 9.0 t ha⁻¹ yr⁻¹ biochar addition, SR: incorporation of wheat straw) and different soil depths (a: 0–5, b: 5–10, c: 10–20, and d: 20–30 cm) during winter wheat season.

<p>Vertical bars represent the standard errors for means of each treatment (<i>n</i> = 3).