Background A comprehensive investigation on the soil organic carbon components and their stability under various vegetation restoration approaches in the loess residual tableland of westernJin Province can provide abundant data support for vegetation restoration projects in ecologically vulnerable areas. Furthermore, it offers a scientific basis for evaluating and implementing the dual-carbon goals in the Loess Plateau.

Methods Taking four different vegetation restoration types in the loess residual tableland as research objects (i.e. Pinus tabulaeformis plantation, Robinia pseudoacacia plantation, Platycladus orientalis plantation and natural secondary forest), the research measured the carbon content of various components at different soil depth levels (0-10, 10-30, 30-60, 60-90, 90-120, 120-150, 150-180, and 180-200 cm), as well as soil bulk density, pH value, moisture content, total nitrogen, total phosphorus, and total potassium during the growing season, employing statistical methods such as principal component analysis, correlation analysis, and network correlation analysis were used to explore the changes in soil organic carbon components and their stability under different vegetation restoration types.

Results 1) In the long-term process of vegetation restoration, the total soil carbon storage in the 0-200 cm layer is ranked as follows: P. tabuliformis plantation > natural secondary forest >P. orientalis plantation >R. pseudoacacia plantation, with respective values of 0.51, 0.44, 0.35, and 0.31 t/hm². Compared to P. tabuliformis plantation and natural secondary forest, the carbon storage is higher. 2) The contents of LFOC and POC in the active organic carbon components, and stable organic carbon components such as HFOC and MOC in the 0-30 cm soil layer of natural secondary forest are the highest, while the highest contents in the 30-200 cm soil layer are found in P. tabuliformis plantation. However, there is no significant change in the contents of LFOC and POC in the soil layers of P. orientalis and R. pseudoacacia plantation. 3) The soil carbon components of the four types of forests are negatively correlated with soil pH, bulk density, and total potassium, and positively correlated with soil total nitrogen, water-soluble organic carbon, total phosphorus, and moisture content. Soil total nitrogen, total phosphorus, and moisture have a positive impact on the accumulation of soil organic carbon components. 4) Through the analysis of soil carbon content in four different types of vegetation restoration for the 0-200 cm soil layer in the Jinxi Loess residual area, it was found that the natural secondary forest and P. tabulaeformis plantation land have the best soil carbon stock and stability, and better water and soil conservation and carbon sequestration benefits.

Conclusions Based on the analysis of soil carbon content of 4 different vegetation restoration types in 0-200 cm soil layer, it was found that the soil carbon pool and its stability were the best in the natural secondary forest and P. tabuliformis plantation in the loess plateau of west Shanxi Province, and the soil and water conservation carbon sequestration benefits were better. In the long run, the vegetation restoration in this study area should prioritize natural recovery, and artificial restoration methods should incorporate P. tabulaeformis plantation as the dominant tree species. The research findings can provide scientific theoretical references and suggestions for vegetation restoration and soil and water conservation practices in ecologically fragile areas.