Original data on the soil properties for afforestation

We selected three paired cropland (control) and adjacent R. pseudoacacia forest (treatment) sites with similar topography and parent materials. Croplands were planted with maize (Zea mays L.) and millet (Setaria italica), whereas forests were dominated by R. pseudoacacia (mean tree density ≈ 2,600 stems ha⁻¹; mean height ≈ 10.4 m). No fertilization or tillage had been applied to forest soils since afforestation. Within each site, one 20 m × 20 m plot was established, and five representative points were randomly chosen for sampling. Soil cores (5 cm diameter) were collected at 20 cm intervals to 1,000 cm depth and composited by depth within each plot. Samples were transported on ice to the laboratory and subdivided for physical, chemical, biochemical, and molecular analyses. We focused on five representative depths (0–20, 180–200, 380–400, 580–600, and 880–900 cm), which capture major gradients in soil moisture and mineral nitrogen along the vertical profile. The relevant soil properties were measured. The data that support the findings of this study are openly available in the Genome Sequence Archive (GSA) at https://ngdc.cncb.ac.cn/gsa, reference number CRA030332.