Soil organic carbon density and its relationship with soil physical properties of typical plantations in South China

Objective  To investigate the effects of Eucalyptus forest and three other stand types in South China on the accumulation of soil organic carbon, and provide a theoretical basis for the management of forest soil carbon pool.

Method  Four kinds of plantations, including E. urophylla, Cunninghamia lanceolate and Pinus massoniana plantations and economic forest, were chosen. Their soil organic carbon content, organic carbon density and the vertical distribution characteristics of organic carbon density in 0–100 cm soil layers were analyzed. The correlations between soil organic carbon and soil physical properties were further analyzed.

Result  For the 0–100 cm soil layer, the soil organic carbon content of four stands ranged from 8.52 to 11.84 g·kg^–1, and the organic carbon density ranged from 2.22 to 3.04 kg·m^–2. Economic forest had the highest soil organic carbon content and density, and there were no significant differences in soil organic carbon content and density among the plantations of E. urophylla, C. lanceolata and P. massoniana. Soil organic carbon content and density in both different stands and different soil depths showed moderate variability. Soil organic carbon content and density decreased with the increase of soil depth, and the organic carbon density of 0–40 cm soil layer accounted for more than 50% of the whole vertical section. The regression coefficient and slope of organic carbon density (y) and organic carbon content (x) showed an increasing trend with the increase of soil depth. Both organic carbon content and density significantly negatively correlated with soil bulk density. The organic carbon content significantly positively correlated with capillary water-holding capacity, total porosity, capillary porosity, non-capillary porosity and aeration porosity. The organic carbon density significantly positively correlated with capillary porosity and non-capillary porosity.

Conclusion  Compared with C. lanceolata and P. massoniana, E. urophylla plantation did not significantly reduce the accumulation of soil organic carbon. Most soil organic carbon was accumulated in the upper soil layer. Soil bulk density, capillary porosity and aeration porosity are all crucial to soil organic carbon accumulation.