Abstract: Soil organic carbon and its components play an important role in carbon cycling of forest ecosystems. In this study, we selected three typical forest types of Eastern Liaoning, including natural secondary forest (broadleaved mixed forest, SF), pure larch plantation forest (LF), and larch and Manchurian ash mixed plantation forest (MF), and collected soil samples of different depths (0-10, 10-20 and 20-30 cm) to analyze the variation of soil organic carbon (TOC) and its active carbon components. The contents of TOC and its active organic carbon in the three forest types all decreased with the increases of soil depth. Among the three forest types, the contents of TOC and its active organic carbon decreased in the sequence of the natural secondary forest > mixed plantation forest > pure plantation forest. The TOC contents in the surface (0-10 cm) were 61.52, 49.22 and 41.16 g·kg^-1, respectively. For active organiccarbon, the contents of particulate organic carbon (POC) were the highest being 20.18, 15.84 and 12.92 g·kg^-1, followed by light fraction organic carbon (LFOC) and microbial biomass carbon (MBC), with the contents being 13.51, 10.04, 8.24 g·kg^-1 and 9.06, 6.13, 5.11 g·kg^-1 respectively. The contents of easily oxidized organic carbon (EOC) were the lowest, being 3.54, 2.78, 2.26 g·kg^-1 in the natural secondary forest, mixed plantation forest, and pure plantation forest, respectively. There were significantly positive relationships between TOC and LFOC, POC, EOC and MBC across the three types of forests (P<0.01).

Key words: slope aspect, Loess Plateau, leaf functional trait, slope gradient, apricot