Figure 3

Variation in permanganate oxidizable carbon (POXC) content in different N-deposition treatments in 0–10 cm (a) and 10–20 cm (b) in spring, summer, and autumn. CK: Control (0 kg N·ha⁻¹ yr⁻¹); LN: low-N deposition (50 kg N·ha⁻¹ yr⁻¹); MN: medium-N deposition (100 kg N·ha⁻¹ yr⁻¹); HN: high-N deposition (150 kg N·ha⁻¹ yr⁻¹). Each value in the plot represents the average value of three plots replicates. The error bars represent the standard error and different letters indicate significant differences among treatments (p < 0.05).