The correlations between soil microbial biomass carbon (MBC) and soil temperature (a), and between MBC and soil water content (SWC, b).

<p>The correlations between soil microbial biomass carbon (MBC) and soil temperature (a), and between MBC and soil water content (SWC, b).</p

The ratio of soil microbial biomass carbon (MBC) to soil microbial biomass nitrogen (MBC/MBN) 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).</p

Coefficients of seasonal variation of MBC under different treatments (%).

<p>Note: Different small letters indicate significant differences among 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) at the P<0.05 level (L.S.D.).</p

Coefficients of seasonal variation of MBN under different treatments (%).

<p>Note: Different small letters indicate significant differences among 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) at the P<0.05 level (L.S.D.).</p

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).</p