| Summary: | Tropical rainforests are the most complex forest ecosystem in the world, and play an important role in the global carbon cycle. To investigate the accumulation characteristics of soil organic carbon (SOC) in tropical rainforests of different origins, soil samples from plantation and natural forests of tropical mountain rainforests in Wuzhi Mountain (WM), Qixian Mountain (QM) and Diaoluo Mountain (DM) in eastern Hainan Island, China, were collected at various depths (0–10, 10–30 and 30–50 cm). SOC concentrations of different-forest-origin soils were analysed and compared, and the effects of soil physicochemical parameters on SOC concentration in natural and plantation forests were investigated. SOC concentrations in plantation forests in WM, QM and DM were higher than those in natural forests, although the difference was not statistically significant. In the 0–50 cm soil depth, the SOC concentrations of different-forest-origin soils decreased with increasing soil depth, with SOC concentrations in the surface layer (0–10 cm) of natural forests being significantly higher than those in the middle layer (10–30 cm) and bottom layer (30–50 cm) (P < 0.05). Natural forests have lower pH than plantation forests. Correlation analysis revealed significant negative correlation (P < 0.05) between SOC concentration in both forest origins and soil pH. The proportion of clay and silt is greater in natural forests than in plantation forests, but the proportion of sand is greater in plantation forests.
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