Fig. 1

Change trends of soil pH values under acid rain stress. The experimental treatments were: CK, control check; S1, pH 4.5, S/N 5:1; S2, pH 3.5, S/N 5:1; S3, pH 2.5, S/N 5:1; SN1, pH 4.5, S/N 1:1; SN2, pH 3.5, S/N 1:1; SN3, pH 2.5, S/N 1:1; N1, pH 4.5, S/N 1:5; N2, pH 3.5, S/N 1:5; N3, pH 2.5, S/N 1:5. Different letters indicate significant difference (p < 0.05) between different treatments in the same season based on one-way ANOVA, followed by a Duncan test. Three-way ANOVA was applied to indicate significant differences between variances (no CK treatments). S/N, the ratio of SO₄²⁻ to NO₃⁻; pH, acid rain pH, ***, ** and * indicate significant differences at p < 0.001, 0.01, and 0.05, respectively