Fig. 1: Effects of nitrogen (N) enrichment on plant and soil biodiversity.

Plots show the effect size of N enrichment on richness (a–c) and Shannon index (d–g) of plant and soil biodiversity across the entire global dataset, within ecosystem types (grasslands, forests, and croplands) and climate zones (tropical, temperate, and boreal). Points and error bars represent mean effect size and 95% confidence intervals (CIs), respectively. The effect sizes (E_ComN, %) are standardized to a common rate (25 kg N ha⁻¹ year⁻¹) and duration (10 years) of N enrichment. When the 95% CIs do not overlap with zero, the effect is significant at P < 0.05 (marked with solid points). Otherwise, the effect is not significant (P > 0.05; open points). Black, green and yellow points indicate the entire dataset, ecosystem types and climate zones attributes, respectively. The number of observations (n) and total number of studies either across the entire dataset or in each ecosystem and climate zone category are displayed in parentheses. The plant species richness and Shannon index are not analyzed for croplands because they are highly modified and managed for agricultural purposes. P value represents the between group differences based on Cochran’s Q test (two-sided tests). Q_B value represents the heterogeneity in effect among groups. The Q_B value with a P < 0.05 indicates significant differences in N effects among ecosystem types or climate zones. Source data are provided as a Source Data file.