Fig. 4

Changes in the relative expression patterns of starch metabolism-related genes [AGPS2b (A, C) and SUS4 (B, D)] at 7, 14, 21, and 28 days after anthesis in response to different biochar and N levels in the early (A, C) and late (B, D) seasons. Different letters above columns indicate significant differences (P < 0.05). Vertical bars represent the standard error of the mean. Note: N1B0–N, lower dose + Control (no biochar); N2B0–N, higher dose + Control (no biochar); N1B1–N, lower dose + Biochar 10 t ha^− 1; N1B2–N,lower dose + Biochar 20 t ha^− 1; N1B3–N, lower dose + Biochar 30 t ha^− 1; N2B1– N, higher dose + Biochar 10 t ha^− 1; N2B2– N, higher dose + Biochar 20 t ha^− 1; and N2B3– N, higher dose + Biochar 30 t ha^− 1