Abstract: We analyzed the effects of meteorological factors and soil properties on vertical variation of SOC, based on soil organic carbon (SOC) density in different soil layers (0-10, 10-20, 20-30, 30-50, and 50-100 cm) from 131 mature natural forests in different climate zones in China. The results showed that SOC density decreased with increasing soil depth (0-30 cm) in temperate coniferous, temperate deciduous broadleaved, subtropical deciduous broadleaved and subtropical evergreen broadleaved forests. There were significant regional variations of SOC density in 0-100 cm soil layer. SOC density of 0-100 cm soil layer in temperate coniferous forests was higher than temperate deciduous broadleaved forests, and was higher in subtropical evergreen broadleaved forests than subtropical deciduous broadleaved forests. SOC density was significantly positively correlated with soil clay content, mean annual precipitation, and aboveground net primary production, and significantly negatively correlated with soil pH and mean annual temperature. Mean annual precipitation and mean annual temperature influenced input and output of SOC, while soil pH and clay content affected SOC accumulation. Therefore, protecting mature natural coniferous and evergreen broadleaved forests would benefit forest carbon sequestration in China.

Key words: soil organic carbon, mature natural forest, random forest model, structural equation model