Invasive soil legacy index (mean ± SE) of Rhus typhina and Ailanthus altissima under three nitrogen addition levels in a monoculture (a) and mixture (b). Differing lowercase letters indicate significant differences according to post-hoc Tukey’s HSD test. The P values represented the result of one-way ANOVA of nitrogen deposition on invasive soil legacy index of invasive R. typhina and native A. altissima. N0: no nitrogen addition; N8: moderate nitrogen addition (8 N m-2 year-1); and N20: high nitrogen addition (20 N m-2 year-1). The colours of the bars represent the nitrogen addition treatments of R. typhina and A. altissima.