Original data

In this study, we determined the soil properties, root traits, and microbial community as well as their correlations in two soil depths in Populus tomentosa, Platycladus orientalis, and Sophora japonica plantations with different forest ages. Our results showed that at the phylum level, the highest relative abundance of soil bacteria and fungi were Actinobacteriota (18.63-32.74%) and Ascomycota (62.48-91.91%), respectively. The Chao, Shannon, and Pielou_e index of fungi in soils increased with forest age, while Alpha diversity of bacteria showed different trends with forest age across species. Redundancy analysis and hierarchical segmentation analysis showed that the effect of soil properties and root traits on composition of soil bacteria (41.4%) was larger than fungi (28.8%). Compared with root traits (7-10 %), soil properties exhibited larger effects (23-26%) on the composition of microbial community. Soil clay, water content, and conductivity showed positive effects on bacterial diversity and composition, while fungi were mainly affected by soil total phosphorus and pH. The influence of root traits on bacterial diversity weakened while that of soil properties increased with forest age. The fungal diversity in middle-aged plantations was affected by soil and root, while that of younger- and older-aged were affected by soil properties. As soil depth increased, the impact of roots on bacterial diversity increased while the effect on fungal diversity decreased. The results highlight the need to consider forest age and soil depth when revealing the association among soil microbial diversity, environmental variation, and root traits.