A profound understanding of the characteristics of soil phosphorus (P) fractions and their influencing factors is crucial for enhancing the productivity of subtropical forest ecosystems. Currently, however, research on quantifying soil P fractions at different depths in diverse plantations using a uniform standard is scarce. Additionally, our comprehension of the driving forces behind the transformation of soil P fractions, particularly microbial factors, is still limited. In this study, four types of planted forests, namely Chinese fir (Cunninghamia lanceolata), eucalyptus (Eucalyptus robusta), Moso bamboo (Phyllostachys edulis), and Masson pine (Pinus massoniana), were selected as the research objects. Soil P fractions, chemical properties, and microbial characteristics of the surface (0-20 cm), middle (20-40 cm), and deep (40-60 cm) soil layers were collected and systematically analyzed. Among the soil P fractions of the four types of planted forests, occluded P and organic P were the main components, accounting for more than 70.0%. Moreover, the contents of various P fractions, as well as the amounts of microbial biomass carbon, microbial biomass nitrogen, microbial biomass P, and the copy numbers of the phoX gene in the surface soil, are all higher than those in the deep soil. In Moso bamboo plantations, the content of available P (5.6-40.3 mg/kg) and secondary mineral P (8.7-57.5 mg/kg) in each soil layer and their proportion in total P (proportion of available phosphorus: 3.9-6.7%; proportion of phosphorus in secondary minerals: 3.3-9.9%) were significantly higher than in the other three types of plantations (P < 0.05). Chinese fir plantations had the highest content of primary mineral P (surface layer: 23.4 mg/kg; middle layer: 17.5 mg/kg; deep layers: 17.0 mg/kg); eucalyptus plantations had the highest content of occluded P (surface layer: 632.2 mg/kg; middle layer: 585.7 mg/kg; deep layers: 535.2 mg/kg), and Masson pine plantations had the lowest content of available P (surface layer: 8.8 mg/kg; middle layer: 6.9 mg/kg; deep layers: 6.8 mg/kg). Microbial biomass P and the phoX gene had a significant impact on soil phosphorus fractions (P < 0.05). These results indicated that the P supply capacity of the soil in Moso bamboo plantations was significantly superior to that in Chinese fir, eucalyptus, and Masson pine plantations. Soil depth was a key factor affecting soil P fractions. Therefore, it is recommended to implement differentiated management for different plantations and to pay attention to the regulatory role of soil depth on the P cycle.