Soil carbon stocks in plantations and natural forests of the sub-tropics

Soil carbon (C) storage plays an important role in the mitigation of atmospheric CO2 emission. Soil C pools under different vegetation are distinct and need to be investigated. However, there are still large quantities of data shortages, which should be remedied by field and systematic studies. Soil was collected at 0–10 cm depth from subtropical natural vegetation and plantations both in southeast China and southeast Queensland, Australia, respectively. Soil samples were assayed for soil organic C; organic N and inorganic N; and mineralization of SOC; total C, N, and P; and pH. Our results suggested soil C concentrations in natural vegetation ranged from 6.25% to 9.20%, whereas soil C concentrations in plantations ranged from 1.08% to 2.69%. No significant differences were found among vegetation along altitudinal gradients, whereas plantations with different tree species had different soil C concentrations, being higher in broadleaf-species plantations than in coniferous-species plantations. But there were no differences in soil C between single-species plantations and mixed-species plantations. Soil C concentrations in plantations were correlated with soil moisture, soil pH and dissolved organic C concentrations; Whereas soil C concentrations in natural vegetation were significantly correlated with soil moisture, soil pH and NO3− concentrations. These results can contribute to the remedy of data shortages and provide the data necessary for model projections and informed decisions in the future.