Abstract:The carbon stock and total organic carbon (TOC) stability in soils of four typical plantations at 25-year-old in South China were investigated. The TOC content, labile carbon pool and soil microbial carbon in soil depth of 0~10 cm and 10~20 cm were determined. The results showed that soil TOC contents were in order as Acacia mangium > Acacia auriculaeformis > Pinus ellettii > Schima superba forest. Legume plantations (A. mangium and A. auriculaeformis) had markedly higher TOC content than non-legumes plantations (P. ellettii and S. superba). The TOC contents in two soil layers of A. mangium plantation were twice as high as those of S. superba plantation. S. superba plantation had the highest labile carbon pool (7.80 mg g-1) and the shortest turnover time (49 d). On the contrast, A. mangium plantation had the lowest labile carbon pool (2.14 mg g-1) and Clab/TOC (8.63%). A. mangium plantation had more stable TOC than other 3 plantations. The microbial carbon contents in surface soil layer (0~10 cm) were in order as A. mangium plantation>P. ellettii plantation>A. auriculaeformis plantation>S. superba plantation. It suggested more microbes favored transformation of litter into soil organic matter. At the subsoil layer (10~20 cm), soil microbial carbon in A. auriculaeformis plantation was significantly higher than those in others forest types, though it was very low in this layer. A. mangium plantation had the lowest microbial carbon content. It suggested that soil TOC accumulation in plantations was closely related to stability of organic matter and quantity of soil microbes.