Abstract: Pinus massoniana is one of the main afforestation species in southwest China, which is sensitive to acid deposition. To cope with acid deposition, stand transformation is often carried out in coniferous forests that have been seriously affected. In this study, we explored the effects of transformation of P. massoniana pure plantation on soil acidification and nutrients by comparing P. massoniana-C. camphora mixed plantation, C. camphora pure plantation, and P. massoniana pure plantation in Tieshanping of Chongqing. Soil samples of humus (Ah) and leachate (E) horizons were collected in different seasons. The results showed that: (1) Forest type had significant effects on soil properties in Ah horizon (P<0.05). Soil nutrient concentrations in Ah horizon were significantly higher than those in E horizon. Soil properties in both horizons varied greatly across seasons (P<0.05). (2) After the transformation of P. massoniana pure plantation, soil pH in Ah horizon was in order of P. massoniana pure plantation < P. massoniana-C. camphora mixed plantation < C. camphora pure plantation. Soil NH₄⁺∶NO₃^- ratio was significantly reduced after the transformation of P. massoniana pure plantation, which could alleviate soil acidification. (3) Soil organic carbon and total nitrogen concentrations were significantly reduced after the transformation of P. massoniana pure plantation, while soil total phosphorus and total potassium concentrations were significantly increased (P<0.05), which could provide more phosphorus and potassium and thus alleviate the phosphorus and potassium limitation on plant growth in the acidic soils. (4) The comprehensive soil fertility index evaluated by the fuzzy comprehensive method was 0.585-0.664. Our results suggested that the transformation of the P. massoniana pure plantation into P. massoniana-C. camphora mixed plantation and C. camphora pure plantation could improve soil fertility.

Key words: soil acidification, Pinus massoniana, Cinnamomum camphora, forest type